Detailed explanation and application parameters of filter technology
OLPF optical low-pass filter
The full name of OLPF is; Optical lowpass filter, The optical low-pass filter is mainly used to filter light signals of different frequencies and wavelengths in the input light, in order to transmit them to the CCD and avoid interference from different frequency signals on the CCD's color interpretation. OLPF has a significant impact on the control of false colors, which mainly come from the main images such as close stripes, fences, or concentric circles. The colors are similar but not the same. When light passes through the lens and reaches the CCD, the color mosaic filter can only distinguish 25% of red and blue and 50% of green, and then the color processing engine uses data difference calculation to integrate them into a complete image.
Due to a shortage of color data in the sky, CCD was unable to determine the parameters of adjacent colors of closely spaced stripes, ultimately leading to engine errors in determining and outputting incorrect colors. Due to the different directions of the fine stripes, corresponding angle optical low-pass filtering chips are required to eliminate them. Additionally, different models of CCD cameras and; CMOS image sensors have some differences in specifications. In order to address the interference noise generated by different models and directions, OLPF designs with different thicknesses, chip numbers, and angle combinations are required to improve image quality.
The role of IR-CUT dual filter switching
The use of IR-CUT dual filters can effectively solve the problem of bimodal filters. The IR-CUT dual filter consists of an infrared cut-off filter and a full spectrum optical glass. When the daytime light is sufficient, the infrared cut-off filter works, and the CCD reproduces the true color. When the nighttime light is insufficient, the infrared cut-off filter automatically moves away, and the full spectrum optical glass begins to work, allowing the CCD to fully utilize all the light and greatly improve low light performance.
IR CUT dual filter specially designed for; CCD cameras correct color cast and out of focus issues, ensuring that captured images are not out of focus or out of focus. Infrared night vision is more transparent, solving the problem of color cast in day and night images of infrared all-in-one cameras. It can filter strong light to make the color of the image pure, beautiful, and softer, achieving visual color consistency for the human eye.
Ordinary day and night cameras use dual peak filters that can transmit a certain proportion of infrared light, which has the advantage of low cost. However, due to the high infrared component in natural light, when it enters the CCD, it will interfere with color reproduction, such as green plants turning gray white, red clothes turning gray green, etc. (especially in outdoor environments with sunlight). Shenzhen Nahong Optoelectronic Technology Co., Ltd. is a professional manufacturer of precision optical filters. At night, due to the filtering effect of the dual peak filter, the CCD cannot fully utilize all the light, and its low illumination performance is unsatisfactory.
Comparison of different effects between using and not using OLPF filters
CCD camera and infrared light
CCD itself is sensitive to infrared light. When using a black and white camera, turn off the lights and use infrared light to illuminate, the image will appear. Why can't the color CCD see infrared? In fact, color; CCD can also detect infrared radiation because it can sense infrared radiation, which can interfere with it; D.S.P The operation of the image processing main chip leads to; Color cast” Therefore, we need to find a way to prevent it from receiving infrared radiation, which is to put on the CCD; Sunglasses” The only difference is that sunglasses worn by people are designed to block ultraviolet rays, while CCD is designed to block infrared rays. This is what color refers to; The filter attached to the CCD This is the transmittance of the filter for each wavelength of light, with the horizontal axis representing wavelength in nanometers (nm) and the vertical axis representing transmittance. We can see that the transmittance from 380nm-645nm is approximately; 93% That's exactly the range of visible light (purple indigo blue green yellow orange red). More than 600; Nm is red light, and to the right of it, it is represented by” External” Let's call it 'rdquo'; Infrared” Yes, it is; Light other than red; It's not red light because the eyes can no longer see it. Also, around 380nm, what we see with our eyes is purple. To the left of 380nm, it appears as; External” Let's call it 'rdquo'; Ultraviolet radiation; We can't see with our eyes, but it can harm our skin Why doesn't the black and white CCD have a filter? Is it not afraid of color interference? Black and white cameras already have no color, how come; Color” Excuse me? So in the early days, infrared cameras used black and white cameras with infrared projection lights Later on, color cameras became more and more common. It was no longer possible to use color cameras during the day and black and white cameras to turn on infrared lights at night. This led to repeated investment. After understanding the principles behind it, someone came up with a method: use color cameras when there is light, remove the filter on the CCD when there is no light, and turn on infrared lights. Day and night infrared color camera; That's how it came out. So, the camera mentioned above has a mechanical structure installed in front of the CCD, which uses an electromagnetic valve to pull or push the filter back, and you can hear it when it is activated; Kacha; One sound Speaking of which, those who have studied optics must notice that CCD with or without a filter will have a different refractive index of light. Removing the filter and applying infrared light will result in a slight difference in refractive index due to different wavelengths, which can cause focal shift; Out of focus; Therefore, as mentioned earlier, we cannot just remove the filter, we also need to add a lens to adjust the refractive index, that is, a filter and a common lens need to be replaced This kind of; Day and night infrared color camera; It was made by the Japanese, it's too expensive. Do you want to imitate it? The mold is expensive and you're afraid of being sued. Some genius bosses even remove the filter, so you can see infrared radiation! Color indoor day night infrared camera; When there is no light at night, just turn on the Infrared light at 850nm can be seen by CCD. 850nm is very close to the wavelength of visible light; 850nm projection lamps often produce a small amount of visible light components, and what is seen is red, which is known as” Red hot” The source. The infrared night vision problem has been solved. Now it's a daytime issue. Since the filter will allow 850nm infrared radiation to leak in, it will cause color interference, which is; Daytime color deviation; The origin of this can only be adjusted through software to minimize color cast in DSP programs
Issues to be noted when using optical low-pass filter OLPF
Please note that improper use of OLPF can result in the following issues:
(1) When the resolution of the lens is higher than that of the CCD image sensor, noise will be generated in the image when viewing images at higher frequencies (beyond the CCD resolution). Use appropriate OLPF can eliminate the noise generated by high frequencies; If inappropriate is used; OLPF， It will cause a decrease in resolution or too much noise.
(2) When the resolution of the lens is insufficient, the resolution of the CCD image sensor cannot be fully utilized, and the function of OLPF will be greatly reduced, which may result in a decrease in resolution. Generally, when customers value resolution, they use thinner OLPF chips; If the customer values the effect of eliminating noise, a thicker OLPF chip. For advanced imaging products, four pieces can be used; Intermediate level products can adopt a two-piece (or three piece) design; Low end products are single piece.
The role of infrared cut-off filter in OLPF filter
When using CCD or; When CMOS image sensors capture color scenes, their response to color is different from that of the human eye. Therefore, it is necessary to remove the infrared parts that can be detected by them but cannot be detected by the human eye, and adjust the response to color within the visible light range to make the colors presented in the image conform to the perception of the human eye. Therefore, generally in; Adding an infrared cut-off filter that only passes visible light in the middle of the OLPF chip, such as phosphate glass (absorption type), can achieve excellent results (widely used by Japanese manufacturers). There are comparative examples of the application of phosphate glass in television monitoring technology, but the image effect is better when using it. Therefore, using infrared cut-off filters can greatly improve image quality. Due to the different refractive index of quartz compared to air, reflection occurs at the interface, reducing the intensity of incident light. To reduce the loss caused by reflection, an anti reflection film AR is generally coated on the chip; Coating is used to improve the transmittance of light, thereby enhancing the image quality.
CCD or; Low pass effect of COMS image sensor
I don't know if you have noticed that when we shoot objects with thin horizontal and vertical stripes, such as when we shoot objects wearing clothing with thin stripes, there will always be thick or thin stripes in the video image, and these stripes will change accordingly with the distance or movement of the object being photographed. This phenomenon is more severe for low-end machines, and high-definition machines are no exception. Recently, after researching some materials, I found that this is due to a special type of image sensor; Low pass effect; As a result. In order to help everyone understand the essence of this issue, we have excerpted and organized a paragraph to explain it for your reference.
Due to CCD or; CMOS solid-state image sensor is a discrete pixel optoelectronic imaging device. According to the Nyquist theorem, the highest spatial frequency that an image sensor can resolve is equal to half of its spatial sampling frequency, which is called the Nyquist limit frequency. When using a CCD camera to obtain target image information, when the sampled image exceeds the Nyquist limit frequency of the system, high-frequency components will be reflected into the fundamental frequency band on the image sensor, causing the so-called ripple effect or Moir é effect, resulting in periodic frequency spectrum overlap and confusion or beat frequency phenomenon in the image. Assuming the sampling frequency of CCD is; 15MHZ， When the image signal is 10MHz, the aliasing frequency component is; 15MHZ-10MHZ=5MHZ， When the image signal is; At 9MHz, the aliasing frequency component is 15MHZ-9MHZ=6MHz. After low-pass filtering by the circuit, both of these aliasing frequency components cannot be filtered out and are output like useful image signals, such as in the observed waveform at 9MHz and; Overlay at 10MHz frequency band; 5MHz and; 6MHz signal component. In There is a noticeable low-frequency beat on the 7MHz signal, with a beat frequency of approximately 1MHz. These mixed signals will affect image clarity and even cause color stripe interference.
Due to the existence of the above phenomenon, television hosts rarely wear clothing with stripes, or in other words, clothing with stripes is a very taboo attire for television workers. Due to small household CCDs or; CMOS camera image sensors transmit optical information in both vertical and horizontal directions using discrete sampling methods, because their photosensitive units are also discrete in the horizontal direction. According to the sampling theorem, the frequency spectrum distribution and amplitude change of the sampled signal are:
In the formula,τ S is the sampling pulse width, which is the width of one photosensitive unit; Ts is the sampling period, which is the width of one pixel (including the non photosensitive parts on both sides). When When n=Ts, the spectral line envelope reaches the first zero point, which is a manifestation of the aperture stop effect. If the amplitude of the high-frequency signal decreases, it can be appropriately selected; τ s， Reduce the amplitude of the spectrum at fs/2 and minimize the aliasing of the spectrum. τ The smaller the value of s, the slower the decrease in spectral amplitude, and the increase in aliasing. As ts increases, the decrease in spectral amplitude accelerates, and the aliasing part of the spectrum decreases. From this, it can be seen that there is an optimal ratio between the width of the photosensitive unit and the pixel width in small household cameras, where the size, density, and number of pixels are the main factors determining the camera resolution. The spectral aliasing reflected in the image can cause low-frequency interference fringes, which have a significant impact on the horizontal clarity of the image captured by the camera.
Due to the difficulty in filtering out interference that is present in useful video images using electronic low-pass filters in electronic circuits, the most commonly used optical lens adopts pre-processing pre filtering technology to reduce the bandwidth of the optical image on the camera's photosensitive surface, thereby reducing spectral confusion. Therefore, optical low-pass filters are used. Optical Low Pass Filter (OLPF) is actually a quartz chip used for low-pass filtering. In 1988, Fuji and Toshiba collaborated to launch the first Digital Still Camera (DSC), which brought OLPF into the rapidly developing digital world.
With the advancement of technology, the application fields of digital imaging technology are becoming increasingly broad, from digital cameras (DSC), digital camcorders (DVC) to video phones and future third-generation mobile phones (G3), all products related to imaging must be used; OLPF is used to eliminate the aforementioned noise interference. Due to the use of this discontinuous imaging method by solid-state image sensors such as cameras, unnecessary interference noise will definitely be generated when capturing fine stripes (high frequencies). Due to the different directions of the fine stripes, it is necessary to use optical low-pass filtering chips with corresponding angles to eliminate them, and also because of the different models of There are some differences in specifications between CCD cameras and CMOS image sensors. To address the interference noise generated by different models and directions, different combinations of thickness, number of chips, and angle are required; The design of OLPF aims to improve the quality of imaging.
Therefore, the lens of a camera is not only used for simple optical imaging, but also for more profound functions such as optical filtering.
Infrared transmission filter (near-infrared)
Comparison of Different Effects Taken with Infrared Cut off Filter and Transmitting Infrared Filter
The shooting effect using a transparent infrared filter
The shooting effect using an infrared cut-off filter
Infrared light and its applications
Infrared radiation IR; light,IR Radiation is electromagnetic radiation within a certain range of wavelengths greater than the red light wavelength, with a wavelength of 780-106nm. It is divided into three bands: near-infrared (IR-A, wavelength 780-1500nm, NIR), mid infrared (IR-B, 1500-6000nm, MIR), and far-infrared (IR-C, 6000-14000nm, FIR). The corresponding infrared light sources are called near-infrared, mid infrared, and far-infrared light sources. Infrared light sources are commonly used for heating, therapy, night vision, communication, navigation, plant cultivation, and livestock breeding. Infrared light was discovered by British scientist Herschel in the laboratory in 1800 It is an electromagnetic wave with a longer wavelength than infrared, which has a significant thermal effect that can be felt but not seen by humans Scientists have discovered that when a certain wavelength of light (visible or invisible) is irradiated onto the surface of certain metals and other materials, they will emit an electron flow, known as the photoelectric effect
Any object in nature is a source of infrared radiation, constantly emitting infrared light from night vision devices By utilizing the photoelectric effect of infrared light, people have developed infrared night vision devices It has two types: energy (equipped with artificial infrared light source), infrared night vision device, and passive Infrared night vision devices project the infrared light emitted (or reflected) by natural objects, which is invisible to the human eye, onto the photocathode of a photoelectric converter through the objective lens of a photoelectric telescope According to the photoelectric effect, an electron current flows out of the photocathode and is rapidly directed towards the positively charged fluorescent screen Scientists have designed an electronic lens that directs electrons along a certain path towards the fluorescent screen while flipping the inverted image flipped by the objective lens back into a positive image In order to better observe the obtained image, an eyepiece is installed between the fluorescent screen and the eyes, so that the nighttime scenery can be clearly seen through a photoelectric telescope
According to the same principle, scientists have also developed infrared cameras and infrared cameras They can not only take pictures and photographs in the dark, but also through thin mist and seawater, and even take pictures of the traces left by people or objects when they first leave Because the temperature of the place where people have stayed is slightly higher than the surrounding area, it can emit slightly stronger infrared light By using these technologies, people can diagnose diseases, detect material damage, scout enemy situations, and so on Nowadays, people can use infrared remote sensing detectors on airplanes and satellites to detect the infrared light emitted by a cigarette butt that fell to the ground in a large forest from high altitude Infrared remote sensing has high resolution and can work day and night, which has been widely used in geological exploration, environmental protection, and military reconnaissance
Filter terminology
Incident angle: The angle between the incident light and the normal of the filter surface. When the light is incident normally, the incident angle is 0 °;.
Spectral characteristics: The spectral parameters of the filter (transmittance T, reflectance R, optical density OD, phase, polarization state s, p, and other characteristics relative to wavelength changes).
Center wavelength: The center of a bandpass filter is called the center wavelength (CWL). The passband width is expressed as the width at half maximum transmittance (FWHM), commonly referred to as half width.
Effective aperture: The physical area effectively utilized in an optical system. Usually, the appearance size of the filter is similar, concentric, and slightly smaller in size.
Cut off position/front back: Cut on corresponds to the spectral characteristics from attenuation to transmission; 50% point, cut-off corresponds to the 50% point of spectral characteristics from transmission to attenuation. Sometimes it can also be defined as the 5% or 10% point of peak transmittance.
Tolerance: Any product has manufacturing tolerances. Taking bandpass filters as an example, there should be a tolerance for the center wavelength and a tolerance for the half width, so it is necessary to indicate the tolerance range when ordering products. The smaller the tolerance, the better the actual use of the filter. The smaller the tolerance, the greater the manufacturing difficulty and the higher the cost. Users can propose reasonable tolerance ranges according to their actual needs.
Long wave pass filter: Interference cut-off filter requires a beam of light within a certain wavelength range to be highly transmitted, while beams that deviate from this wavelength range suddenly become highly reflected (or suppressed) It has a wide range of applications. Usually, we refer to the filter that suppresses the transmission of short waves through long waves as a long wave pass filter, and vice versa as a short wave pass filter.
CCD camera and infrared light
CCD itself is sensitive to infrared light. When using a black and white camera, turn off the lights and use infrared light to illuminate, the image will appear. Why can't the color CCD see infrared? In fact, color; CCD can also detect infrared radiation because it can sense infrared radiation, which can interfere with it; D.S.P The operation of the image processing main chip leads to; Color cast” Therefore, we need to find a way to prevent it from receiving infrared radiation, which is to put on the CCD; Sunglasses” The only difference is that sunglasses worn by people are designed to block ultraviolet rays, while CCD is designed to block infrared rays. This is what color refers to; The filter attached to the CCD This is the transmittance of the filter for each wavelength of light, with the horizontal axis representing wavelength in nanometers (nm) and the vertical axis representing transmittance. We can see that the transmittance from 380nm-645nm is approximately; 93% That's exactly the range of visible light (purple indigo blue green yellow orange red). More than 600; Nm is red light, and to the right of it, it is represented by” External” Let's call it 'rdquo'; Infrared” Yes, it is; Light other than red; It's not red light because the eyes can no longer see it. Also, around 380nm, what we see with our eyes is purple; 380nm to the left; External” Let's call it 'rdquo'; Ultraviolet radiation; We can't see with our eyes, but it can harm our skin Why doesn't the black and white CCD have a filter? Is it not afraid of color interference? Black and white cameras already have no color, how come; Color” Excuse me? So in the early days, infrared cameras used black and white cameras with infrared projection lights Later on, color cameras became more and more common. It was no longer possible to use color cameras during the day and black and white cameras to turn on infrared lights at night. This led to repeated investment. After understanding the principles behind it, someone came up with a method: use color cameras when there is light, remove the filter on the CCD when there is no light, and turn on infrared lights. Day and night infrared color camera; That's how it came out. So, the camera mentioned above has a mechanical structure installed in front of the CCD, which uses an electromagnetic valve to pull or push the filter back, and you can hear it when it is activated; Kacha; One sound Speaking of which, those who have studied optics must notice that CCD with or without a filter will have a different refractive index of light. Removing the filter and applying infrared light will result in a slight difference in refractive index due to different wavelengths, which can cause focal shift; Out of focus; Therefore, as mentioned earlier, we cannot just remove the filter, we also need to add a lens to adjust the refractive index, that is, a filter and a common lens need to be replaced This kind of; Day and night infrared color camera; It was made by the Japanese, it's too expensive. Do you want to imitate it? The mold is expensive and you're afraid of being sued. Some genius bosses even remove the filter, so you can see infrared radiation! Color indoor day night infrared camera; When there is no light at night, just turn on the Infrared light at 850nm can be seen by CCD. 850nm is very close to the wavelength of visible light; 850nm projection lamps often produce a small amount of visible light components, and what is seen is red, which is known as” Red hot” The source. The infrared night vision problem has been solved. Now it's a daytime issue. Since the filter will allow 850nm infrared radiation to leak in, it will cause color interference, which is; Daytime color deviation; The origin of this can only be adjusted through software to minimize color cast in DSP programs
What is PC material
PC is the abbreviation for polycarbonate, and the English name for polycarbonate is; Polycarbonate， Abbreviation PC engineering plastic, PC material is actually one of the engineering plastics we refer to. As a widely used material worldwide, PC has its own characteristics and advantages and disadvantages. PC is an amorphous thermoplastic resin with excellent comprehensive performance, including excellent electrical insulation, elongation, dimensional stability, chemical corrosion resistance, high strength, heat resistance, and cold resistance; It also has the advantages of self extinguishing, flame retardant, non-toxic, and colorable. You can see the shadow of PC plastic in every corner of your life. The characteristics of large-scale industrial production and easy processing also make its price extremely low. Its strength can meet various needs from mobile phones to bulletproof glass, but its disadvantage is that it lacks hardness compared to metal, which makes its appearance easier to scratch. However, its strength and toughness are good, whether it is heavy pressure or general falls, as long as you don't try to hit it with a stone, it is long enough to last
What is PET material?
Polydimethylene phthalate is the most common type of thermoplastic polyester, also known as polyethylene; Terephthalate abbreviation; PET or PETP (also known as PET), commonly known as polyester resin, is a condensed polymer of terephthalic acid and ethylene glycol, collectively referred to as thermoplastic polyester or saturated polyester along with PBT.
In 1946, Britain published the first preparation; PET patent, UK, 1949; ICI company completed the pilot test, but after DuPont purchased the patent, a production facility was established in 1953, which was the first in the world to achieve industrial production. In the early days, PET was almost exclusively used for synthetic fibers (commonly known as polyester or Dacron in China). Since the 1980s, PET has made breakthrough progress as an engineering plastic, with the continuous development of nucleating agents and crystallization promoters. Currently, PET is; PBT, together with thermoplastic polyester, has become one of the five major engineering plastics.
The production scale of PET in our country lags far behind several major foreign manufacturers. Enter In the 1980s, China gradually introduced advanced PET resin synthesis equipment ranging from tens of thousands to hundreds of thousands of tons from abroad, resulting in significant progress in both quality and output. According to statistics from the China Textile Society, in 1997, China produced PET chip resin; 1.74 million tons, of which the production capacity of sliced resin for high viscosity packaging (such as beverage bottles and packaging sheets) is 224000 tons, so the production is; The source of PET engineering plastic grade resin is abundant. Due to the fact that the equipment for preparing various mixed modified PET plastics is universal compared to other polymer mixing modification equipment, and the manufacturing of domestic mixed extruder machines has also formed a certain scale, once the market is developed, the production of PET plastics in China will also grow rapidly. Characteristics and Applications of Polyethylene Terephthalate (PET) 1. Characteristics PET is a highly crystalline polymer with a milky white or bright yellow color, with a smooth and glossy surface. Good resistance to creep, fatigue, friction, and dimensional stability, with low wear and high hardness, possessing the highest toughness among thermoplastic materials; Good electrical insulation performance, less affected by temperature, but poor corona resistance. Non toxic, weather resistant, chemically stable, low water absorption, resistant to weak acids and organic solvents, but not resistant to hot water immersion or alkali. The glass transition temperature of PET resin is high, the crystallization rate is slow, the molding cycle is long, the molding cycle is long, the molding shrinkage rate is large, the dimensional stability is poor, the crystallization molding is brittle, and the heat resistance is low.
Through the improvement of nucleating agents, crystallization agents, and glass fiber reinforcement, PET not only has; In addition to the properties of PBT, there are also the following characteristics:
1. The thermal deformation temperature and long-term use temperature are the highest among thermoplastic general engineering plastics;
2. Due to its high heat resistance, it enhances; PET in Immersing in a 250 ℃ soldering bath for 10 seconds, there is almost no deformation or discoloration, making it particularly suitable for preparing electronic and electrical components for soldering;
3. Bending strength; 200MPa， The elastic modulus reaches 4000MPa, and the creep and fatigue resistance are also good. The surface hardness is high, and the mechanical properties are similar to thermosetting plastics;
4. Due to production; The ratio of ethylene glycol used in PET production; The price of polybutylene glycol used in PBT is almost half cheaper, so PET resin and reinforcement; PET is the lowest priced engineering plastic and has a high cost performance ratio.
2、 Application
PET is mainly used for fibers, with a small amount used for films and engineering plastics. PET fibers are mainly used in the textile industry. PET film is mainly used for electrical insulation materials, such as capacitors, cable insulation, printed circuit wiring substrates, electrode slot insulation, etc. Another application area of PET film is substrate and baseband, such as film, X-ray film, recording tape, electronic computer tape, etc. PET film is also used to vacuum transfer aluminum to make metalized films, such as gold and silver wires, micro capacitor films, etc. Another use of PET is blow molded products, used for packaging polyester stretch bottles.
Fiberglass reinforced PET is suitable for the electronic, electrical, and automotive industries, used for various coil frames, transformers, televisions, recorder components and casings, automotive lamp sockets, lampshades, incandescent lamp sockets, relays, selenium rectifiers, etc. The current consumption ratios of PET engineering plastics in several application fields are: electrical and electronic 26%, automotive 22%, machinery 19%, appliances 10%, consumer goods 10%, and others 13%. At present, the total consumption of PET engineering plastics is not large, accounting for only; Total amount of PET; 1.6%
What is PMMA material? The chemical name for PMMA is polymethyl methacrylate, and common products include acrylic, acrylic, and acrylic; (Both are the Chinese names for acrylic in English), which actually translates to organic glass! Polymethyl methacrylate (PMMA) has extremely superior optical properties and is a highly transparent thermoplastic that has been widely used. PMMA products include various types such as plates, tubes, rods, and molding compounds, mainly used in aviation, radio, instruments, meters, medical equipment, decoration, indication, advertising, and other fields. Due to the disadvantages of low surface hardness, easy scratching, low impact resistance, and poor formability of PMMA, modifications of PMMA have emerged one after another. Such as copolymerization of methyl methacrylate with styrene and butadiene, PMMA with; PC blending, etc. Super Transparent; PMMA material is mainly used for mobile phone protective screens. This product is divided into two types: those with hardened coating and those without hardened coating Its characteristics are excellent light transmittance, no impurities, electrostatic protective film, and a surface hardening thickness that can reach hardness; PMMA materials with a hardness of 5-6H or higher are currently highly recommended for hardening treatment and are referred to as "PMMA" in China; Raw board;.
1、 The main properties of polymethyl methacrylate are:
PMMA is a colorless and transparent glassy substance with a specific gravity; 1.19, with low surface hardness, easily scratched by hard objects. Difficult to ignite, but able to burn slowly and continue to burn even after leaving the fire. It is prone to fragmentation, melting and dripping, and has a bright flame with a blue bottom and a white top, emitting a strong floral and fruity odor as well as a rotten vegetable odor.
1. Transparency: PMMA is an amorphous polymer, and the arrangement of its internal molecules does not interfere with the speed of light passing through its various parts. Therefore, it can make light travel at the same speed (i.e. uniform refractive index), without causing light to scatter and interfere with each other on all sides. So PMMA has excellent optical properties, high transmittance (90-92%, wavelength dependent). A sheet or rod with a smooth surface can reflect all the light rays that enter from one end inside it when bent to a certain extent, and finally exit from the other end, just like water flowing through a pipe (a certain degree of curvature refers to the angle formed by the bent position and the original position, which cannot exceed 42 degrees);; When bending in an arc shape, the radius of the arc must be greater than the diameter of the rod or the thickness of the sheet; 3 times). But when a certain part of its surface is roughened, light can escape from here and display brightness. This characteristic can be utilized to manufacture edge emitting devices, surgical medical instruments, etc.
2. Mechanical properties: PMMA has higher mechanical strength than ordinary glass; More than 10 times, but compared to other plastics, its strength can only be considered moderate. Its disadvantages are light and brittle weight, easy cracking (or silver lines), low surface hardness, and easy scratching and loss of luster; The wear resistance is poor, with a static friction coefficient of 0.8 between them and a dynamic friction coefficient of 0.45-0.50 for steel, making it easy to scratch and grind.
3. Electrical performance: PMMA has good electrical performance, especially under low-frequency working conditions. However, some of its electrical properties are unique: the dielectric loss tangent decreases with increasing frequency. Temperature and frequency have an impact on the dielectric constant, while climate and humidity have little effect on electrical performance. But the electrical performance ratio; PE, PS, etc.
4. Thermal performance: The heat resistance of PMMA is not good enough, and the operating temperature is only; 80 ℃. It can be copolymerized and crosslinked with monomers such as ethylene glycol acrylate or propylene methacrylate to improve heat resistance. The specific heat of PMMA is lower than most thermoplastic materials, which is beneficial for its rapid thermal plasticization. In addition, it also has a certain degree of cold resistance, with little change in impact strength at low temperatures of -50 to -60 ℃.
5. Chemical properties; PMMA has a certain degree of chemical corrosion resistance, but it weakens with increasing temperature. Has strong resistance to chemical corrosion of gases, and has not been corroded by long-term contact with ozone and sulfur dioxide; Chlorine gas can corrode its surface. Can dissolve in ethyl or butyl acetate, glacial acetic acid, chloroform, benzene, etc; It can adsorb various alcohol organic compounds, causing volume expansion and rough and hairy surface, but is insoluble in aliphatic compounds.
6. Climate resistance: It has excellent weather resistance and little change in transparency and color after years of exposure to tropical climate.
Molding and processing of polymethyl methacrylate (PMMA):
1. Processing characteristics of PMMA:
At the processing temperature, the rheological properties of PMMA melt are basically close to non Newtonian type, which means that its melt viscosity is mainly controlled by pressure (shear rate). Therefore, to reduce viscosity and increase fluidity, it is mainly achieved by increasing pressure. However, its melt viscosity ratio; PE, PS, etc. are much higher, so the pressure required for injection molding is high. Moreover, its melt viscosity decreases with increasing temperature, making it more sensitive to temperature than other thermoplastic materials. Therefore, it is necessary to control the temperature well in order to facilitate molding.
⑵ PMMA pellets are prone to moisture absorption in air, up to a maximum of; 3%. It must be dried before molding, otherwise bubbles will be generated. More attention should be paid when using recycled materials.
Due to PMMA being an amorphous polymer, its molding shrinkage rate is small, which is; 0.5-1.8%.
Due to the high viscosity and poor fluidity of PMMA melt, as well as the fast cooling rate, the product is prone to internal stress. Therefore, the molding process of PMMA requires strict requirements, and the mold design requirements are high. The product generally requires post-treatment. PMMA products are prone to silver streaks during storage and use; The appearance of silver lines is a prerequisite for brittle fracture of glassy polymers. The rupture of substances in silver lines causes the initiation and expansion of cracks, ultimately leading to fracture. Silver lines are caused by internal stress in the material, so attention should be paid to reducing or avoiding them during molding, that is, having sufficient insulation time during molding.
2. Injection molding processing of PMMA:
⑴ Drying: The temperature should be lower than its thermal deformation temperature; 10-20 ℃ (100-110 ℃), drying time of about 2-8 hours (drying to moisture content); 0.02-0.04%). Dried materials should not be exposed to air and should be stored in a sealed hopper.
⑵ Injection temperature: generally between 180-220 ℃ ⑶ Injection pressure: 80-130MPa ⑶ Mold temperature: 40-60 ℃ ⑶ Mold runner should be thick and short, and the use of sprues should be avoided as much as possible, otherwise the sprue diameter should not be less than; 1.5mm
A bandpass filter is an optical component that allows light of a specific wavelength to pass through while reflecting (or attenuating) light of other wavelengths. The working area of a bandpass filter can be in the ultraviolet, visible, near-infrared, and far-infrared bands, depending on your application scope. Compared with conventional cut-off filters or color filters, designing and manufacturing bandpass filters is more difficult, mainly because the positions of the spectral peaks at both ends need to be precisely controlled. Controlling the position of two points is certainly much more difficult than controlling one point.
A bandpass filter is a type of glass with a relatively narrow bandwidth and clear cutoff for short and long waves. Its spectral characteristics are represented by the maximum transmittance (TM) and its wavelength (λ M) position, the short wave cutoff wavelength, the long wave cutoff wavelength, and the half width. The wavelength corresponding to half of the maximum transmittanceλ 1 and λ The difference between 2 (λ 1-λ 1) nm is called the full width at half maximum (FWHM).
Mirror shaped beam splitter is an optical window with a semi transparent mirror shaped film coated on its surface, which can decompose a beam of light into two or more beams of light. A beam splitter reflects a portion of the incident light energy, absorbs a relatively small portion, and transmits the remaining energy. The spectrophotometer has obvious neutral color characteristics. A spectroscope is made by vacuum evaporation of multiple layers of dielectric films, without the problem of absorption by metal films, and the total ratio of penetration and reflection is close to that of a metal film; 100. Function: Made by vacuum evaporation, the light passing through the filter can change the penetration ratio, for example, it can penetrate half and reflect half, with low absorption characteristics.
Principles, Characteristics, and Applications of IPL Technology
IPL(Intense Pulsed Light) It is a high-intensity, broad-spectrum, discontinuous light source with a wavelength range between 530nm-1200nm, also known as strong pulsed light. Photon belongs to photothermal therapy, which is a non-invasive and non-invasive therapy. Photon skin rejuvenation technology uses intense pulsed light (IPL) to directly irradiate the skin, generating photobiochemical reactions. On the one hand, it can regenerate collagen fibers and elastic fibers in the skin, rearrange them, restore skin elasticity, improve facial microcirculation, and remove or reduce wrinkles; On the other hand, strong pulsed light can penetrate the skin and be selectively absorbed by pigment groups and capillaries in the tissue. Thermal energy causes blood coagulation without damaging normal skin tissue, and pigment groups are thermally decomposed and destroyed. It can treat capillary dilation, remove pigmentation, and remove excess hair from the face. Skin treatment, improvement 560nm-1200nm, 590nm-1200nm, 640nm-1200nm hair removal hair loss 695nm-1200nm, 645nm-1200nm, 755nm-1200nm
IPL technology advantages
1. The treatment takes about 15-30 minutes, and the whole process is fast, simple, and painless. There is no discomfort after treatment, and you can immediately wash your face and apply makeup without rest.
2. During treatment, a special treatment head is used to release uniform pulsed light towards the treatment area. The treatment headband has a unique cooling device to protect the skin from damage, and special filter glasses are worn without worrying about eye injury. The entire treatment process is completed in a very safe manner.
3. Due to different symptoms, a course of treatment usually involves 4-6 sessions, with a three week interval between each session. After the first treatment, you will feel that your skin is smoother and the color is more uniform. The expected result is facial congestion, redness, and a gradual decrease in capillary dilation. There is obvious signs of sun aging as fine wrinkles decrease, pore size shrinks, and sun pigmentation spots fade. The skin becomes smoother, and many patients with rosacea can see significant improvement and their lesions decrease or terminate. Achieve optimal results with each treatment. Going back in time, the rejuvenation of youth is no longer our dream. The IPL light guide produced by Ruicheng Optoelectronics can be customized according to customer requirements; K9 glass, made of quartz or sapphire material, can be used for photon rejuvenation machines, photon beauty devices, photon therapy devices, IPL treatment equipment. The spot size (coating surface) and transmission wavelength can be customized according to requirements.
The function of an anti reflection filter is to reduce light reflection and increase penetration intensity. Wherever there is a desire to enhance the penetration intensity of light, it exists. Due to the widespread use of various sheets for surface protection in front of display systems, the surface has a reflectivity of about 10%, resulting in environmental reflection and a decrease in the display level of the entire system. Our company provides various specifications of anti reflective plastic sheets, reducing the reflectivity from 10% to 1%, making it an ideal choice for protecting display windows.
Working principle of anti reflection film (anti reflection film)
Light has wave particle duality, which means that at the microscopic level, it can be understood as both a wave and a beam of high-speed moving particles (note that it should not be understood as a simple wave or a simple particle here. They are all microscopic in nature. The wavelength of red light waves is 0.750 micrometers, and the wavelength of purple light waves is 0.400 micrometers). The mass of a photon is; 6.63E-34 kilograms It seems that they are far from the macroscopic waves and particles we imagine ）The principle of anti reflection film is to consider light as a wave, because light waves, like mechanical waves, also have the property of interference. Apply a layer of anti reflective film in front of the lens (usually; Calcium fluoride; If the thickness of the film is equal to one fourth of the wavelength of red light (note: red light) in the anti reflective film, the red light reflected back on both sides of this film will interfere and cancel each other out. You will not see any reflection in front of the lens because the beam of red light has already passed through the lens Why have I never seen a lens without reflection? The reason is simple, because visible light has; Red, orange, yellow, green, blue, indigo, purple; There are seven colors, and the thickness of the film is unique, so only one color of light can be taken care of to allow it to fully enter the lens. Generally, all green light is allowed to enter. In this case, the color reflected by the lens in visible light is blue purple because there is no green light in this reflected light. The thickness of the film can also be determined based on the color characteristics of the lens.
Definition and Design:
The discovery of anti reflective films in the 1930s promoted the early development of thin film optics. For the promotion of technical optics, anti reflective films also play the most important role among all optical films. Even today, in terms of their total production, they still exceed all other films. Therefore, studying the design and preparation techniques of anti reflective films is of great significance for production practice
We all know that when light enters a medium with a refractive index n0, the refractive index is; When the other medium is n1, light reflection will occur at the interface between the two media. If the medium does not absorb, the interface is an optical surface, and the light is incident vertically, then the reflectivity R is the transmittance
For example, the refractive index is 1. 52 crown glass, with a reflection of approximately on each surface; About 4.2%. The surface reflection of flint glass with a higher refractive index is more significant. This surface reflection causes two serious consequences: loss of light energy, which reduces the brightness of the image; The surface reflected light undergoes multiple reflections or diffusion, and some of it becomes stray light, which eventually reaches the image plane, reducing the contrast of the image and affecting the imaging quality of the system. Especially for complex systems such as television and film photography lenses, which cover many surfaces adjacent to the air, without an anti reflection film, they will be completely unusable. At present, there are many different types of anti reflection films available to meet the needs of a large part of the technical optics field. However, complex optical systems and laser optics often have special and strict requirements for anti reflection performance. For example, high-power laser systems require certain components to have extremely low surface reflection to avoid damage to sensitive components by unwanted reflections. In addition, broadband anti reflection films improve image quality, color balance, and operating distance, enhancing the overall performance of the system. Therefore, the practical needs of production have prompted the continuous development of anti reflection films
In complex optical systems, the energy of incident light is often lost due to multiple reflections. For example, the lens of a high-end camera consists of six or seven lenses. The reflected loss of light energy accounts for about half of the incident light energy, and the reflected stray light also affects the quality of imaging. In order to reduce the loss caused by the reflection of incident light energy on the surface of the lens glass, a uniformly thick transparent film (usually magnesium fluoride MgF2, with a refractive index of 1.38, between glass and air) is often coated on the mirror surface. The interference of the film is used to minimize the reflected light energy, and such a film is called an anti reflection film.
Now let's take a look at a simple single-layer anti reflective film. Assuming the thickness of the film is e, when light is incident vertically, the optical path difference of the reflected light on the two surfaces of the film is; 2ne， Due to the phase transition during reflection on both the upper and lower surfaces of the film, there is no additional phase difference. When the two reflected lights interfere and cancel each other out, the following conditions should be met:
Single layer anti reflective film
The minimum thickness of the membrane should be (corresponding to k=0)
Due to the cancellation of reflected light, transmitted light is strengthened.
A single-layer anti reflective film can only make a specific wavelengthλ Minimize the reflection of light as much as possible, and there may be varying degrees of attenuation for other reflected light of similar wavelengths, but not to the weakest. For general cameras and visual optical instruments, the wavelength most sensitive to the human eye is often selected as lambda; =550nm as'; Control wavelength; When viewing the reflected light of this film under white light, yellow and green colors are the weakest, while red and blue colors are relatively stronger, resulting in a basket purple mirror surface. Some optical devices require reducing their transmittance to increase the intensity of reflected light. The resonant cavity mirror in helium neon lasers requires wavelengthλ =The reflectivity of 632.8nm monochromatic light reaches; More than 99%. If a low refractive index film is replaced with a high refractive index film of the same thickness, the interference between the two reflected lights on the upper and lower surfaces of the film is strengthened, which enhances the reflected light and weakens the transmitted light. Such a film is called an anti reflective film or a high reflective film. A typical single-layer anti reflection film can increase the reflectivity to over 30%, while a multi-layer anti reflection film can increase it even more. Due to the low absorption of light by this dielectric film, it has a better reflective effect than silver plated or aluminum plated mirrors.
The full name of OLPF is; Optical lowpass filter, The optical low-pass filter is mainly used to filter light signals of different frequencies and wavelengths in the input light, in order to transmit them to the CCD and avoid interference from different frequency signals on the CCD's color interpretation. OLPF has a significant impact on the control of false colors, which mainly come from the main images such as close stripes, fences, or concentric circles. The colors are similar but not the same. When light passes through the lens and reaches the CCD, the color mosaic filter can only distinguish 25% of red and blue and 50% of green, and then the color processing engine uses data difference calculation to integrate them into a complete image.
Due to a shortage of color data in the sky, CCD was unable to determine the parameters of adjacent colors of closely spaced stripes, ultimately leading to engine errors in determining and outputting incorrect colors. Due to the different directions of the fine stripes, corresponding angle optical low-pass filtering chips are required to eliminate them. Additionally, different models of CCD cameras and; CMOS image sensors have some differences in specifications. In order to address the interference noise generated by different models and directions, OLPF designs with different thicknesses, chip numbers, and angle combinations are required to improve image quality.
The role of IR-CUT dual filter switching
The use of IR-CUT dual filters can effectively solve the problem of bimodal filters. The IR-CUT dual filter consists of an infrared cut-off filter and a full spectrum optical glass. When the daytime light is sufficient, the infrared cut-off filter works, and the CCD reproduces the true color. When the nighttime light is insufficient, the infrared cut-off filter automatically moves away, and the full spectrum optical glass begins to work, allowing the CCD to fully utilize all the light and greatly improve low light performance.
IR CUT dual filter specially designed for; CCD cameras correct color cast and out of focus issues, ensuring that captured images are not out of focus or out of focus. Infrared night vision is more transparent, solving the problem of color cast in day and night images of infrared all-in-one cameras. It can filter strong light to make the color of the image pure, beautiful, and softer, achieving visual color consistency for the human eye.
Ordinary day and night cameras use dual peak filters that can transmit a certain proportion of infrared light, which has the advantage of low cost. However, due to the high infrared component in natural light, when it enters the CCD, it will interfere with color reproduction, such as green plants turning gray white, red clothes turning gray green, etc. (especially in outdoor environments with sunlight). Shenzhen Nahong Optoelectronic Technology Co., Ltd. is a professional manufacturer of precision optical filters. At night, due to the filtering effect of the dual peak filter, the CCD cannot fully utilize all the light, and its low illumination performance is unsatisfactory.
Comparison of different effects between using and not using OLPF filters
CCD camera and infrared light
CCD itself is sensitive to infrared light. When using a black and white camera, turn off the lights and use infrared light to illuminate, the image will appear. Why can't the color CCD see infrared? In fact, color; CCD can also detect infrared radiation because it can sense infrared radiation, which can interfere with it; D.S.P The operation of the image processing main chip leads to; Color cast” Therefore, we need to find a way to prevent it from receiving infrared radiation, which is to put on the CCD; Sunglasses” The only difference is that sunglasses worn by people are designed to block ultraviolet rays, while CCD is designed to block infrared rays. This is what color refers to; The filter attached to the CCD This is the transmittance of the filter for each wavelength of light, with the horizontal axis representing wavelength in nanometers (nm) and the vertical axis representing transmittance. We can see that the transmittance from 380nm-645nm is approximately; 93% That's exactly the range of visible light (purple indigo blue green yellow orange red). More than 600; Nm is red light, and to the right of it, it is represented by” External” Let's call it 'rdquo'; Infrared” Yes, it is; Light other than red; It's not red light because the eyes can no longer see it. Also, around 380nm, what we see with our eyes is purple. To the left of 380nm, it appears as; External” Let's call it 'rdquo'; Ultraviolet radiation; We can't see with our eyes, but it can harm our skin Why doesn't the black and white CCD have a filter? Is it not afraid of color interference? Black and white cameras already have no color, how come; Color” Excuse me? So in the early days, infrared cameras used black and white cameras with infrared projection lights Later on, color cameras became more and more common. It was no longer possible to use color cameras during the day and black and white cameras to turn on infrared lights at night. This led to repeated investment. After understanding the principles behind it, someone came up with a method: use color cameras when there is light, remove the filter on the CCD when there is no light, and turn on infrared lights. Day and night infrared color camera; That's how it came out. So, the camera mentioned above has a mechanical structure installed in front of the CCD, which uses an electromagnetic valve to pull or push the filter back, and you can hear it when it is activated; Kacha; One sound Speaking of which, those who have studied optics must notice that CCD with or without a filter will have a different refractive index of light. Removing the filter and applying infrared light will result in a slight difference in refractive index due to different wavelengths, which can cause focal shift; Out of focus; Therefore, as mentioned earlier, we cannot just remove the filter, we also need to add a lens to adjust the refractive index, that is, a filter and a common lens need to be replaced This kind of; Day and night infrared color camera; It was made by the Japanese, it's too expensive. Do you want to imitate it? The mold is expensive and you're afraid of being sued. Some genius bosses even remove the filter, so you can see infrared radiation! Color indoor day night infrared camera; When there is no light at night, just turn on the Infrared light at 850nm can be seen by CCD. 850nm is very close to the wavelength of visible light; 850nm projection lamps often produce a small amount of visible light components, and what is seen is red, which is known as” Red hot” The source. The infrared night vision problem has been solved. Now it's a daytime issue. Since the filter will allow 850nm infrared radiation to leak in, it will cause color interference, which is; Daytime color deviation; The origin of this can only be adjusted through software to minimize color cast in DSP programs
Issues to be noted when using optical low-pass filter OLPF
Please note that improper use of OLPF can result in the following issues:
(1) When the resolution of the lens is higher than that of the CCD image sensor, noise will be generated in the image when viewing images at higher frequencies (beyond the CCD resolution). Use appropriate OLPF can eliminate the noise generated by high frequencies; If inappropriate is used; OLPF， It will cause a decrease in resolution or too much noise.
(2) When the resolution of the lens is insufficient, the resolution of the CCD image sensor cannot be fully utilized, and the function of OLPF will be greatly reduced, which may result in a decrease in resolution. Generally, when customers value resolution, they use thinner OLPF chips; If the customer values the effect of eliminating noise, a thicker OLPF chip. For advanced imaging products, four pieces can be used; Intermediate level products can adopt a two-piece (or three piece) design; Low end products are single piece.
The role of infrared cut-off filter in OLPF filter
When using CCD or; When CMOS image sensors capture color scenes, their response to color is different from that of the human eye. Therefore, it is necessary to remove the infrared parts that can be detected by them but cannot be detected by the human eye, and adjust the response to color within the visible light range to make the colors presented in the image conform to the perception of the human eye. Therefore, generally in; Adding an infrared cut-off filter that only passes visible light in the middle of the OLPF chip, such as phosphate glass (absorption type), can achieve excellent results (widely used by Japanese manufacturers). There are comparative examples of the application of phosphate glass in television monitoring technology, but the image effect is better when using it. Therefore, using infrared cut-off filters can greatly improve image quality. Due to the different refractive index of quartz compared to air, reflection occurs at the interface, reducing the intensity of incident light. To reduce the loss caused by reflection, an anti reflection film AR is generally coated on the chip; Coating is used to improve the transmittance of light, thereby enhancing the image quality.
CCD or; Low pass effect of COMS image sensor
I don't know if you have noticed that when we shoot objects with thin horizontal and vertical stripes, such as when we shoot objects wearing clothing with thin stripes, there will always be thick or thin stripes in the video image, and these stripes will change accordingly with the distance or movement of the object being photographed. This phenomenon is more severe for low-end machines, and high-definition machines are no exception. Recently, after researching some materials, I found that this is due to a special type of image sensor; Low pass effect; As a result. In order to help everyone understand the essence of this issue, we have excerpted and organized a paragraph to explain it for your reference.
Due to CCD or; CMOS solid-state image sensor is a discrete pixel optoelectronic imaging device. According to the Nyquist theorem, the highest spatial frequency that an image sensor can resolve is equal to half of its spatial sampling frequency, which is called the Nyquist limit frequency. When using a CCD camera to obtain target image information, when the sampled image exceeds the Nyquist limit frequency of the system, high-frequency components will be reflected into the fundamental frequency band on the image sensor, causing the so-called ripple effect or Moir é effect, resulting in periodic frequency spectrum overlap and confusion or beat frequency phenomenon in the image. Assuming the sampling frequency of CCD is; 15MHZ， When the image signal is 10MHz, the aliasing frequency component is; 15MHZ-10MHZ=5MHZ， When the image signal is; At 9MHz, the aliasing frequency component is 15MHZ-9MHZ=6MHz. After low-pass filtering by the circuit, both of these aliasing frequency components cannot be filtered out and are output like useful image signals, such as in the observed waveform at 9MHz and; Overlay at 10MHz frequency band; 5MHz and; 6MHz signal component. In There is a noticeable low-frequency beat on the 7MHz signal, with a beat frequency of approximately 1MHz. These mixed signals will affect image clarity and even cause color stripe interference.
Due to the existence of the above phenomenon, television hosts rarely wear clothing with stripes, or in other words, clothing with stripes is a very taboo attire for television workers. Due to small household CCDs or; CMOS camera image sensors transmit optical information in both vertical and horizontal directions using discrete sampling methods, because their photosensitive units are also discrete in the horizontal direction. According to the sampling theorem, the frequency spectrum distribution and amplitude change of the sampled signal are:
In the formula,τ S is the sampling pulse width, which is the width of one photosensitive unit; Ts is the sampling period, which is the width of one pixel (including the non photosensitive parts on both sides). When When n=Ts, the spectral line envelope reaches the first zero point, which is a manifestation of the aperture stop effect. If the amplitude of the high-frequency signal decreases, it can be appropriately selected; τ s， Reduce the amplitude of the spectrum at fs/2 and minimize the aliasing of the spectrum. τ The smaller the value of s, the slower the decrease in spectral amplitude, and the increase in aliasing. As ts increases, the decrease in spectral amplitude accelerates, and the aliasing part of the spectrum decreases. From this, it can be seen that there is an optimal ratio between the width of the photosensitive unit and the pixel width in small household cameras, where the size, density, and number of pixels are the main factors determining the camera resolution. The spectral aliasing reflected in the image can cause low-frequency interference fringes, which have a significant impact on the horizontal clarity of the image captured by the camera.
Due to the difficulty in filtering out interference that is present in useful video images using electronic low-pass filters in electronic circuits, the most commonly used optical lens adopts pre-processing pre filtering technology to reduce the bandwidth of the optical image on the camera's photosensitive surface, thereby reducing spectral confusion. Therefore, optical low-pass filters are used. Optical Low Pass Filter (OLPF) is actually a quartz chip used for low-pass filtering. In 1988, Fuji and Toshiba collaborated to launch the first Digital Still Camera (DSC), which brought OLPF into the rapidly developing digital world.
With the advancement of technology, the application fields of digital imaging technology are becoming increasingly broad, from digital cameras (DSC), digital camcorders (DVC) to video phones and future third-generation mobile phones (G3), all products related to imaging must be used; OLPF is used to eliminate the aforementioned noise interference. Due to the use of this discontinuous imaging method by solid-state image sensors such as cameras, unnecessary interference noise will definitely be generated when capturing fine stripes (high frequencies). Due to the different directions of the fine stripes, it is necessary to use optical low-pass filtering chips with corresponding angles to eliminate them, and also because of the different models of There are some differences in specifications between CCD cameras and CMOS image sensors. To address the interference noise generated by different models and directions, different combinations of thickness, number of chips, and angle are required; The design of OLPF aims to improve the quality of imaging.
Therefore, the lens of a camera is not only used for simple optical imaging, but also for more profound functions such as optical filtering.
Infrared transmission filter (near-infrared)
Comparison of Different Effects Taken with Infrared Cut off Filter and Transmitting Infrared Filter
The shooting effect using a transparent infrared filter
The shooting effect using an infrared cut-off filter
Infrared light and its applications
Infrared radiation IR; light,IR Radiation is electromagnetic radiation within a certain range of wavelengths greater than the red light wavelength, with a wavelength of 780-106nm. It is divided into three bands: near-infrared (IR-A, wavelength 780-1500nm, NIR), mid infrared (IR-B, 1500-6000nm, MIR), and far-infrared (IR-C, 6000-14000nm, FIR). The corresponding infrared light sources are called near-infrared, mid infrared, and far-infrared light sources. Infrared light sources are commonly used for heating, therapy, night vision, communication, navigation, plant cultivation, and livestock breeding. Infrared light was discovered by British scientist Herschel in the laboratory in 1800 It is an electromagnetic wave with a longer wavelength than infrared, which has a significant thermal effect that can be felt but not seen by humans Scientists have discovered that when a certain wavelength of light (visible or invisible) is irradiated onto the surface of certain metals and other materials, they will emit an electron flow, known as the photoelectric effect
Any object in nature is a source of infrared radiation, constantly emitting infrared light from night vision devices By utilizing the photoelectric effect of infrared light, people have developed infrared night vision devices It has two types: energy (equipped with artificial infrared light source), infrared night vision device, and passive Infrared night vision devices project the infrared light emitted (or reflected) by natural objects, which is invisible to the human eye, onto the photocathode of a photoelectric converter through the objective lens of a photoelectric telescope According to the photoelectric effect, an electron current flows out of the photocathode and is rapidly directed towards the positively charged fluorescent screen Scientists have designed an electronic lens that directs electrons along a certain path towards the fluorescent screen while flipping the inverted image flipped by the objective lens back into a positive image In order to better observe the obtained image, an eyepiece is installed between the fluorescent screen and the eyes, so that the nighttime scenery can be clearly seen through a photoelectric telescope
According to the same principle, scientists have also developed infrared cameras and infrared cameras They can not only take pictures and photographs in the dark, but also through thin mist and seawater, and even take pictures of the traces left by people or objects when they first leave Because the temperature of the place where people have stayed is slightly higher than the surrounding area, it can emit slightly stronger infrared light By using these technologies, people can diagnose diseases, detect material damage, scout enemy situations, and so on Nowadays, people can use infrared remote sensing detectors on airplanes and satellites to detect the infrared light emitted by a cigarette butt that fell to the ground in a large forest from high altitude Infrared remote sensing has high resolution and can work day and night, which has been widely used in geological exploration, environmental protection, and military reconnaissance
Filter terminology
Incident angle: The angle between the incident light and the normal of the filter surface. When the light is incident normally, the incident angle is 0 °;.
Spectral characteristics: The spectral parameters of the filter (transmittance T, reflectance R, optical density OD, phase, polarization state s, p, and other characteristics relative to wavelength changes).
Center wavelength: The center of a bandpass filter is called the center wavelength (CWL). The passband width is expressed as the width at half maximum transmittance (FWHM), commonly referred to as half width.
Effective aperture: The physical area effectively utilized in an optical system. Usually, the appearance size of the filter is similar, concentric, and slightly smaller in size.
Cut off position/front back: Cut on corresponds to the spectral characteristics from attenuation to transmission; 50% point, cut-off corresponds to the 50% point of spectral characteristics from transmission to attenuation. Sometimes it can also be defined as the 5% or 10% point of peak transmittance.
Tolerance: Any product has manufacturing tolerances. Taking bandpass filters as an example, there should be a tolerance for the center wavelength and a tolerance for the half width, so it is necessary to indicate the tolerance range when ordering products. The smaller the tolerance, the better the actual use of the filter. The smaller the tolerance, the greater the manufacturing difficulty and the higher the cost. Users can propose reasonable tolerance ranges according to their actual needs.
Long wave pass filter: Interference cut-off filter requires a beam of light within a certain wavelength range to be highly transmitted, while beams that deviate from this wavelength range suddenly become highly reflected (or suppressed) It has a wide range of applications. Usually, we refer to the filter that suppresses the transmission of short waves through long waves as a long wave pass filter, and vice versa as a short wave pass filter.
CCD camera and infrared light
CCD itself is sensitive to infrared light. When using a black and white camera, turn off the lights and use infrared light to illuminate, the image will appear. Why can't the color CCD see infrared? In fact, color; CCD can also detect infrared radiation because it can sense infrared radiation, which can interfere with it; D.S.P The operation of the image processing main chip leads to; Color cast” Therefore, we need to find a way to prevent it from receiving infrared radiation, which is to put on the CCD; Sunglasses” The only difference is that sunglasses worn by people are designed to block ultraviolet rays, while CCD is designed to block infrared rays. This is what color refers to; The filter attached to the CCD This is the transmittance of the filter for each wavelength of light, with the horizontal axis representing wavelength in nanometers (nm) and the vertical axis representing transmittance. We can see that the transmittance from 380nm-645nm is approximately; 93% That's exactly the range of visible light (purple indigo blue green yellow orange red). More than 600; Nm is red light, and to the right of it, it is represented by” External” Let's call it 'rdquo'; Infrared” Yes, it is; Light other than red; It's not red light because the eyes can no longer see it. Also, around 380nm, what we see with our eyes is purple; 380nm to the left; External” Let's call it 'rdquo'; Ultraviolet radiation; We can't see with our eyes, but it can harm our skin Why doesn't the black and white CCD have a filter? Is it not afraid of color interference? Black and white cameras already have no color, how come; Color” Excuse me? So in the early days, infrared cameras used black and white cameras with infrared projection lights Later on, color cameras became more and more common. It was no longer possible to use color cameras during the day and black and white cameras to turn on infrared lights at night. This led to repeated investment. After understanding the principles behind it, someone came up with a method: use color cameras when there is light, remove the filter on the CCD when there is no light, and turn on infrared lights. Day and night infrared color camera; That's how it came out. So, the camera mentioned above has a mechanical structure installed in front of the CCD, which uses an electromagnetic valve to pull or push the filter back, and you can hear it when it is activated; Kacha; One sound Speaking of which, those who have studied optics must notice that CCD with or without a filter will have a different refractive index of light. Removing the filter and applying infrared light will result in a slight difference in refractive index due to different wavelengths, which can cause focal shift; Out of focus; Therefore, as mentioned earlier, we cannot just remove the filter, we also need to add a lens to adjust the refractive index, that is, a filter and a common lens need to be replaced This kind of; Day and night infrared color camera; It was made by the Japanese, it's too expensive. Do you want to imitate it? The mold is expensive and you're afraid of being sued. Some genius bosses even remove the filter, so you can see infrared radiation! Color indoor day night infrared camera; When there is no light at night, just turn on the Infrared light at 850nm can be seen by CCD. 850nm is very close to the wavelength of visible light; 850nm projection lamps often produce a small amount of visible light components, and what is seen is red, which is known as” Red hot” The source. The infrared night vision problem has been solved. Now it's a daytime issue. Since the filter will allow 850nm infrared radiation to leak in, it will cause color interference, which is; Daytime color deviation; The origin of this can only be adjusted through software to minimize color cast in DSP programs
What is PC material
PC is the abbreviation for polycarbonate, and the English name for polycarbonate is; Polycarbonate， Abbreviation PC engineering plastic, PC material is actually one of the engineering plastics we refer to. As a widely used material worldwide, PC has its own characteristics and advantages and disadvantages. PC is an amorphous thermoplastic resin with excellent comprehensive performance, including excellent electrical insulation, elongation, dimensional stability, chemical corrosion resistance, high strength, heat resistance, and cold resistance; It also has the advantages of self extinguishing, flame retardant, non-toxic, and colorable. You can see the shadow of PC plastic in every corner of your life. The characteristics of large-scale industrial production and easy processing also make its price extremely low. Its strength can meet various needs from mobile phones to bulletproof glass, but its disadvantage is that it lacks hardness compared to metal, which makes its appearance easier to scratch. However, its strength and toughness are good, whether it is heavy pressure or general falls, as long as you don't try to hit it with a stone, it is long enough to last
What is PET material?
Polydimethylene phthalate is the most common type of thermoplastic polyester, also known as polyethylene; Terephthalate abbreviation; PET or PETP (also known as PET), commonly known as polyester resin, is a condensed polymer of terephthalic acid and ethylene glycol, collectively referred to as thermoplastic polyester or saturated polyester along with PBT.
In 1946, Britain published the first preparation; PET patent, UK, 1949; ICI company completed the pilot test, but after DuPont purchased the patent, a production facility was established in 1953, which was the first in the world to achieve industrial production. In the early days, PET was almost exclusively used for synthetic fibers (commonly known as polyester or Dacron in China). Since the 1980s, PET has made breakthrough progress as an engineering plastic, with the continuous development of nucleating agents and crystallization promoters. Currently, PET is; PBT, together with thermoplastic polyester, has become one of the five major engineering plastics.
The production scale of PET in our country lags far behind several major foreign manufacturers. Enter In the 1980s, China gradually introduced advanced PET resin synthesis equipment ranging from tens of thousands to hundreds of thousands of tons from abroad, resulting in significant progress in both quality and output. According to statistics from the China Textile Society, in 1997, China produced PET chip resin; 1.74 million tons, of which the production capacity of sliced resin for high viscosity packaging (such as beverage bottles and packaging sheets) is 224000 tons, so the production is; The source of PET engineering plastic grade resin is abundant. Due to the fact that the equipment for preparing various mixed modified PET plastics is universal compared to other polymer mixing modification equipment, and the manufacturing of domestic mixed extruder machines has also formed a certain scale, once the market is developed, the production of PET plastics in China will also grow rapidly. Characteristics and Applications of Polyethylene Terephthalate (PET) 1. Characteristics PET is a highly crystalline polymer with a milky white or bright yellow color, with a smooth and glossy surface. Good resistance to creep, fatigue, friction, and dimensional stability, with low wear and high hardness, possessing the highest toughness among thermoplastic materials; Good electrical insulation performance, less affected by temperature, but poor corona resistance. Non toxic, weather resistant, chemically stable, low water absorption, resistant to weak acids and organic solvents, but not resistant to hot water immersion or alkali. The glass transition temperature of PET resin is high, the crystallization rate is slow, the molding cycle is long, the molding cycle is long, the molding shrinkage rate is large, the dimensional stability is poor, the crystallization molding is brittle, and the heat resistance is low.
Through the improvement of nucleating agents, crystallization agents, and glass fiber reinforcement, PET not only has; In addition to the properties of PBT, there are also the following characteristics:
1. The thermal deformation temperature and long-term use temperature are the highest among thermoplastic general engineering plastics;
2. Due to its high heat resistance, it enhances; PET in Immersing in a 250 ℃ soldering bath for 10 seconds, there is almost no deformation or discoloration, making it particularly suitable for preparing electronic and electrical components for soldering;
3. Bending strength; 200MPa， The elastic modulus reaches 4000MPa, and the creep and fatigue resistance are also good. The surface hardness is high, and the mechanical properties are similar to thermosetting plastics;
4. Due to production; The ratio of ethylene glycol used in PET production; The price of polybutylene glycol used in PBT is almost half cheaper, so PET resin and reinforcement; PET is the lowest priced engineering plastic and has a high cost performance ratio.
2、 Application
PET is mainly used for fibers, with a small amount used for films and engineering plastics. PET fibers are mainly used in the textile industry. PET film is mainly used for electrical insulation materials, such as capacitors, cable insulation, printed circuit wiring substrates, electrode slot insulation, etc. Another application area of PET film is substrate and baseband, such as film, X-ray film, recording tape, electronic computer tape, etc. PET film is also used to vacuum transfer aluminum to make metalized films, such as gold and silver wires, micro capacitor films, etc. Another use of PET is blow molded products, used for packaging polyester stretch bottles.
Fiberglass reinforced PET is suitable for the electronic, electrical, and automotive industries, used for various coil frames, transformers, televisions, recorder components and casings, automotive lamp sockets, lampshades, incandescent lamp sockets, relays, selenium rectifiers, etc. The current consumption ratios of PET engineering plastics in several application fields are: electrical and electronic 26%, automotive 22%, machinery 19%, appliances 10%, consumer goods 10%, and others 13%. At present, the total consumption of PET engineering plastics is not large, accounting for only; Total amount of PET; 1.6%
What is PMMA material? The chemical name for PMMA is polymethyl methacrylate, and common products include acrylic, acrylic, and acrylic; (Both are the Chinese names for acrylic in English), which actually translates to organic glass! Polymethyl methacrylate (PMMA) has extremely superior optical properties and is a highly transparent thermoplastic that has been widely used. PMMA products include various types such as plates, tubes, rods, and molding compounds, mainly used in aviation, radio, instruments, meters, medical equipment, decoration, indication, advertising, and other fields. Due to the disadvantages of low surface hardness, easy scratching, low impact resistance, and poor formability of PMMA, modifications of PMMA have emerged one after another. Such as copolymerization of methyl methacrylate with styrene and butadiene, PMMA with; PC blending, etc. Super Transparent; PMMA material is mainly used for mobile phone protective screens. This product is divided into two types: those with hardened coating and those without hardened coating Its characteristics are excellent light transmittance, no impurities, electrostatic protective film, and a surface hardening thickness that can reach hardness; PMMA materials with a hardness of 5-6H or higher are currently highly recommended for hardening treatment and are referred to as "PMMA" in China; Raw board;.
1、 The main properties of polymethyl methacrylate are:
PMMA is a colorless and transparent glassy substance with a specific gravity; 1.19, with low surface hardness, easily scratched by hard objects. Difficult to ignite, but able to burn slowly and continue to burn even after leaving the fire. It is prone to fragmentation, melting and dripping, and has a bright flame with a blue bottom and a white top, emitting a strong floral and fruity odor as well as a rotten vegetable odor.
1. Transparency: PMMA is an amorphous polymer, and the arrangement of its internal molecules does not interfere with the speed of light passing through its various parts. Therefore, it can make light travel at the same speed (i.e. uniform refractive index), without causing light to scatter and interfere with each other on all sides. So PMMA has excellent optical properties, high transmittance (90-92%, wavelength dependent). A sheet or rod with a smooth surface can reflect all the light rays that enter from one end inside it when bent to a certain extent, and finally exit from the other end, just like water flowing through a pipe (a certain degree of curvature refers to the angle formed by the bent position and the original position, which cannot exceed 42 degrees);; When bending in an arc shape, the radius of the arc must be greater than the diameter of the rod or the thickness of the sheet; 3 times). But when a certain part of its surface is roughened, light can escape from here and display brightness. This characteristic can be utilized to manufacture edge emitting devices, surgical medical instruments, etc.
2. Mechanical properties: PMMA has higher mechanical strength than ordinary glass; More than 10 times, but compared to other plastics, its strength can only be considered moderate. Its disadvantages are light and brittle weight, easy cracking (or silver lines), low surface hardness, and easy scratching and loss of luster; The wear resistance is poor, with a static friction coefficient of 0.8 between them and a dynamic friction coefficient of 0.45-0.50 for steel, making it easy to scratch and grind.
3. Electrical performance: PMMA has good electrical performance, especially under low-frequency working conditions. However, some of its electrical properties are unique: the dielectric loss tangent decreases with increasing frequency. Temperature and frequency have an impact on the dielectric constant, while climate and humidity have little effect on electrical performance. But the electrical performance ratio; PE, PS, etc.
4. Thermal performance: The heat resistance of PMMA is not good enough, and the operating temperature is only; 80 ℃. It can be copolymerized and crosslinked with monomers such as ethylene glycol acrylate or propylene methacrylate to improve heat resistance. The specific heat of PMMA is lower than most thermoplastic materials, which is beneficial for its rapid thermal plasticization. In addition, it also has a certain degree of cold resistance, with little change in impact strength at low temperatures of -50 to -60 ℃.
5. Chemical properties; PMMA has a certain degree of chemical corrosion resistance, but it weakens with increasing temperature. Has strong resistance to chemical corrosion of gases, and has not been corroded by long-term contact with ozone and sulfur dioxide; Chlorine gas can corrode its surface. Can dissolve in ethyl or butyl acetate, glacial acetic acid, chloroform, benzene, etc; It can adsorb various alcohol organic compounds, causing volume expansion and rough and hairy surface, but is insoluble in aliphatic compounds.
6. Climate resistance: It has excellent weather resistance and little change in transparency and color after years of exposure to tropical climate.
Molding and processing of polymethyl methacrylate (PMMA):
1. Processing characteristics of PMMA:
At the processing temperature, the rheological properties of PMMA melt are basically close to non Newtonian type, which means that its melt viscosity is mainly controlled by pressure (shear rate). Therefore, to reduce viscosity and increase fluidity, it is mainly achieved by increasing pressure. However, its melt viscosity ratio; PE, PS, etc. are much higher, so the pressure required for injection molding is high. Moreover, its melt viscosity decreases with increasing temperature, making it more sensitive to temperature than other thermoplastic materials. Therefore, it is necessary to control the temperature well in order to facilitate molding.
⑵ PMMA pellets are prone to moisture absorption in air, up to a maximum of; 3%. It must be dried before molding, otherwise bubbles will be generated. More attention should be paid when using recycled materials.
Due to PMMA being an amorphous polymer, its molding shrinkage rate is small, which is; 0.5-1.8%.
Due to the high viscosity and poor fluidity of PMMA melt, as well as the fast cooling rate, the product is prone to internal stress. Therefore, the molding process of PMMA requires strict requirements, and the mold design requirements are high. The product generally requires post-treatment. PMMA products are prone to silver streaks during storage and use; The appearance of silver lines is a prerequisite for brittle fracture of glassy polymers. The rupture of substances in silver lines causes the initiation and expansion of cracks, ultimately leading to fracture. Silver lines are caused by internal stress in the material, so attention should be paid to reducing or avoiding them during molding, that is, having sufficient insulation time during molding.
2. Injection molding processing of PMMA:
⑴ Drying: The temperature should be lower than its thermal deformation temperature; 10-20 ℃ (100-110 ℃), drying time of about 2-8 hours (drying to moisture content); 0.02-0.04%). Dried materials should not be exposed to air and should be stored in a sealed hopper.
⑵ Injection temperature: generally between 180-220 ℃ ⑶ Injection pressure: 80-130MPa ⑶ Mold temperature: 40-60 ℃ ⑶ Mold runner should be thick and short, and the use of sprues should be avoided as much as possible, otherwise the sprue diameter should not be less than; 1.5mm
A bandpass filter is an optical component that allows light of a specific wavelength to pass through while reflecting (or attenuating) light of other wavelengths. The working area of a bandpass filter can be in the ultraviolet, visible, near-infrared, and far-infrared bands, depending on your application scope. Compared with conventional cut-off filters or color filters, designing and manufacturing bandpass filters is more difficult, mainly because the positions of the spectral peaks at both ends need to be precisely controlled. Controlling the position of two points is certainly much more difficult than controlling one point.
A bandpass filter is a type of glass with a relatively narrow bandwidth and clear cutoff for short and long waves. Its spectral characteristics are represented by the maximum transmittance (TM) and its wavelength (λ M) position, the short wave cutoff wavelength, the long wave cutoff wavelength, and the half width. The wavelength corresponding to half of the maximum transmittanceλ 1 and λ The difference between 2 (λ 1-λ 1) nm is called the full width at half maximum (FWHM).
Mirror shaped beam splitter is an optical window with a semi transparent mirror shaped film coated on its surface, which can decompose a beam of light into two or more beams of light. A beam splitter reflects a portion of the incident light energy, absorbs a relatively small portion, and transmits the remaining energy. The spectrophotometer has obvious neutral color characteristics. A spectroscope is made by vacuum evaporation of multiple layers of dielectric films, without the problem of absorption by metal films, and the total ratio of penetration and reflection is close to that of a metal film; 100. Function: Made by vacuum evaporation, the light passing through the filter can change the penetration ratio, for example, it can penetrate half and reflect half, with low absorption characteristics.
Principles, Characteristics, and Applications of IPL Technology
IPL(Intense Pulsed Light) It is a high-intensity, broad-spectrum, discontinuous light source with a wavelength range between 530nm-1200nm, also known as strong pulsed light. Photon belongs to photothermal therapy, which is a non-invasive and non-invasive therapy. Photon skin rejuvenation technology uses intense pulsed light (IPL) to directly irradiate the skin, generating photobiochemical reactions. On the one hand, it can regenerate collagen fibers and elastic fibers in the skin, rearrange them, restore skin elasticity, improve facial microcirculation, and remove or reduce wrinkles; On the other hand, strong pulsed light can penetrate the skin and be selectively absorbed by pigment groups and capillaries in the tissue. Thermal energy causes blood coagulation without damaging normal skin tissue, and pigment groups are thermally decomposed and destroyed. It can treat capillary dilation, remove pigmentation, and remove excess hair from the face. Skin treatment, improvement 560nm-1200nm, 590nm-1200nm, 640nm-1200nm hair removal hair loss 695nm-1200nm, 645nm-1200nm, 755nm-1200nm
IPL technology advantages
1. The treatment takes about 15-30 minutes, and the whole process is fast, simple, and painless. There is no discomfort after treatment, and you can immediately wash your face and apply makeup without rest.
2. During treatment, a special treatment head is used to release uniform pulsed light towards the treatment area. The treatment headband has a unique cooling device to protect the skin from damage, and special filter glasses are worn without worrying about eye injury. The entire treatment process is completed in a very safe manner.
3. Due to different symptoms, a course of treatment usually involves 4-6 sessions, with a three week interval between each session. After the first treatment, you will feel that your skin is smoother and the color is more uniform. The expected result is facial congestion, redness, and a gradual decrease in capillary dilation. There is obvious signs of sun aging as fine wrinkles decrease, pore size shrinks, and sun pigmentation spots fade. The skin becomes smoother, and many patients with rosacea can see significant improvement and their lesions decrease or terminate. Achieve optimal results with each treatment. Going back in time, the rejuvenation of youth is no longer our dream. The IPL light guide produced by Ruicheng Optoelectronics can be customized according to customer requirements; K9 glass, made of quartz or sapphire material, can be used for photon rejuvenation machines, photon beauty devices, photon therapy devices, IPL treatment equipment. The spot size (coating surface) and transmission wavelength can be customized according to requirements.
The function of an anti reflection filter is to reduce light reflection and increase penetration intensity. Wherever there is a desire to enhance the penetration intensity of light, it exists. Due to the widespread use of various sheets for surface protection in front of display systems, the surface has a reflectivity of about 10%, resulting in environmental reflection and a decrease in the display level of the entire system. Our company provides various specifications of anti reflective plastic sheets, reducing the reflectivity from 10% to 1%, making it an ideal choice for protecting display windows.
Working principle of anti reflection film (anti reflection film)
Light has wave particle duality, which means that at the microscopic level, it can be understood as both a wave and a beam of high-speed moving particles (note that it should not be understood as a simple wave or a simple particle here. They are all microscopic in nature. The wavelength of red light waves is 0.750 micrometers, and the wavelength of purple light waves is 0.400 micrometers). The mass of a photon is; 6.63E-34 kilograms It seems that they are far from the macroscopic waves and particles we imagine ）The principle of anti reflection film is to consider light as a wave, because light waves, like mechanical waves, also have the property of interference. Apply a layer of anti reflective film in front of the lens (usually; Calcium fluoride; If the thickness of the film is equal to one fourth of the wavelength of red light (note: red light) in the anti reflective film, the red light reflected back on both sides of this film will interfere and cancel each other out. You will not see any reflection in front of the lens because the beam of red light has already passed through the lens Why have I never seen a lens without reflection? The reason is simple, because visible light has; Red, orange, yellow, green, blue, indigo, purple; There are seven colors, and the thickness of the film is unique, so only one color of light can be taken care of to allow it to fully enter the lens. Generally, all green light is allowed to enter. In this case, the color reflected by the lens in visible light is blue purple because there is no green light in this reflected light. The thickness of the film can also be determined based on the color characteristics of the lens.
Definition and Design:
The discovery of anti reflective films in the 1930s promoted the early development of thin film optics. For the promotion of technical optics, anti reflective films also play the most important role among all optical films. Even today, in terms of their total production, they still exceed all other films. Therefore, studying the design and preparation techniques of anti reflective films is of great significance for production practice
We all know that when light enters a medium with a refractive index n0, the refractive index is; When the other medium is n1, light reflection will occur at the interface between the two media. If the medium does not absorb, the interface is an optical surface, and the light is incident vertically, then the reflectivity R is the transmittance
For example, the refractive index is 1. 52 crown glass, with a reflection of approximately on each surface; About 4.2%. The surface reflection of flint glass with a higher refractive index is more significant. This surface reflection causes two serious consequences: loss of light energy, which reduces the brightness of the image; The surface reflected light undergoes multiple reflections or diffusion, and some of it becomes stray light, which eventually reaches the image plane, reducing the contrast of the image and affecting the imaging quality of the system. Especially for complex systems such as television and film photography lenses, which cover many surfaces adjacent to the air, without an anti reflection film, they will be completely unusable. At present, there are many different types of anti reflection films available to meet the needs of a large part of the technical optics field. However, complex optical systems and laser optics often have special and strict requirements for anti reflection performance. For example, high-power laser systems require certain components to have extremely low surface reflection to avoid damage to sensitive components by unwanted reflections. In addition, broadband anti reflection films improve image quality, color balance, and operating distance, enhancing the overall performance of the system. Therefore, the practical needs of production have prompted the continuous development of anti reflection films
In complex optical systems, the energy of incident light is often lost due to multiple reflections. For example, the lens of a high-end camera consists of six or seven lenses. The reflected loss of light energy accounts for about half of the incident light energy, and the reflected stray light also affects the quality of imaging. In order to reduce the loss caused by the reflection of incident light energy on the surface of the lens glass, a uniformly thick transparent film (usually magnesium fluoride MgF2, with a refractive index of 1.38, between glass and air) is often coated on the mirror surface. The interference of the film is used to minimize the reflected light energy, and such a film is called an anti reflection film.
Now let's take a look at a simple single-layer anti reflective film. Assuming the thickness of the film is e, when light is incident vertically, the optical path difference of the reflected light on the two surfaces of the film is; 2ne， Due to the phase transition during reflection on both the upper and lower surfaces of the film, there is no additional phase difference. When the two reflected lights interfere and cancel each other out, the following conditions should be met:
Single layer anti reflective film
The minimum thickness of the membrane should be (corresponding to k=0)
Due to the cancellation of reflected light, transmitted light is strengthened.
A single-layer anti reflective film can only make a specific wavelengthλ Minimize the reflection of light as much as possible, and there may be varying degrees of attenuation for other reflected light of similar wavelengths, but not to the weakest. For general cameras and visual optical instruments, the wavelength most sensitive to the human eye is often selected as lambda; =550nm as'; Control wavelength; When viewing the reflected light of this film under white light, yellow and green colors are the weakest, while red and blue colors are relatively stronger, resulting in a basket purple mirror surface. Some optical devices require reducing their transmittance to increase the intensity of reflected light. The resonant cavity mirror in helium neon lasers requires wavelengthλ =The reflectivity of 632.8nm monochromatic light reaches; More than 99%. If a low refractive index film is replaced with a high refractive index film of the same thickness, the interference between the two reflected lights on the upper and lower surfaces of the film is strengthened, which enhances the reflected light and weakens the transmitted light. Such a film is called an anti reflective film or a high reflective film. A typical single-layer anti reflection film can increase the reflectivity to over 30%, while a multi-layer anti reflection film can increase it even more. Due to the low absorption of light by this dielectric film, it has a better reflective effect than silver plated or aluminum plated mirrors.