From the UV side filters are normally blocked up to X-ray spectrum. From the IR side the blocking range is determined by the sensitivity of a photodetector. The residual transmission of the filters is usually less than 0.1 %, but it can be made as low as 0.01-0.001 % when needed. It should be noted than the smaller is the region of blocking, the higher is the maximum transmission value Tmax achieved. The ultra-violet filters, as a rule, are blocked as far as 700-1100 nm at Tmax = 30-50 %, while filters designed to operate in the 1500-5000 nm range can be disabled up to far IR at Tmax = 55-65 %.
Of great importance is the filter transmission peak shape, which is determined by the coating layer structure. The characteristic of the filter transmission peak shape is the ratio 0.1/0.5 which usually is varied from 3 to 1.25, the transmission peak shape is being approximately rectangular (see pic. 1).
The filters are protected against atmospheric humidity (moisture resistance tests are carried out at a humidity of 98 % and temperature of 40°C during 120 hours). Under operating conditions where the humidity is not higher than 70 %, atmospheric pressure 600-700 Torrs, temperature 5-35°C, the guaranteed preservation period for the ratings is 3 years.
The production-run filters have diameters of 10.5, 20.7, 31, 41, and 50.8 mm and clear apertures 7, 16, 26, 35, and 46 mm, accordingly.
Pic.1. Spectral characteristic of interference filter.
Pic.2. Transmission peak shape for different ratio 0.1/0.5 values: 3 (1), 1.7 (2), 1.25 (3).
The Table shows typical parameters of some filters used to select laser emission lines.