Deep ultraviolet narrowband filters should use ferrules

Deep ultraviolet filters are required in many situations. Narrow band filters at 220nm and 275nm are used in total nitrogen detection instruments that measure the total nitrogen content in water using photometry. For example, narrow band filters at 254nm, 265nm, 280nm, and other day blind levels are used in forensic testing.

Due to the scarcity of materials that can transmit deep ultraviolet wavelengths below 300nm in nature, metal induced coating technology is generally used to produce deep ultraviolet filters. This involves mixing aluminum with a medium and controlling the thickness of the aluminum film and medium to achieve transmission in the ultraviolet wavelength band and cutoff in other wavelengths.

We know that aluminum is a very reactive metal that easily combines with water vapor or oxygen in the air to undergo chemical reactions, turning aluminum into aluminum oxide or hydroxide. Therefore, in order to prolong the lifespan of induced filters, it is necessary to consciously control the oxidation rate of aluminum and isolate the aluminum film.

This kind of isolation cannot be achieved simply by gluing the film layer together, as there is no glue that can penetrate the deep ultraviolet band. For these reasons, the sealing of deep ultraviolet filters is done using side sealing methods.

Some manufacturers directly stack two pieces of glass with film surfaces and seal the sides with sealant. This method has a short lifespan for the filter because the water vapor or oxygen between the two film surfaces in direct contact is difficult to escape and is adsorbed on the film surface. Over time, a considerable chemical reaction occurs, resulting in the appearance of spots on the film surface. So, the induced membrane layer cannot directly contact other interfaces. At present, most manufacturers use structures with high requirements for side coating, and if not careful, air may still leak in.

Ruicheng Optoelectronics has excellent sealing technology performance for deep ultraviolet filters. Its packaging structure greatly reduces the difficulty of coating, and the sealing performance of the filter is particularly good, which means that the service life of the filter is very long. After customer inspection, it will not attenuate the optical transmittance for 3 years.

Regardless of the sealing structure used, overall, deep ultraviolet filters generally require a sleeve to be attached and sealed on the side. This type of filter has a long service life and is reliable.

Ruicheng Optoelectronics has been committed to developing high-performance precision filters. Please feel free to inquire.