Band-pass optical filters

Figure 11.18. The ruby fluorescence lifetime-based fiber optic thermometer system. Fi short-pass optical filter Ft /f-line band pass optical filter.

The spectral dependence of the light sensitivity (as indicated by yellowing) of free films of Parylene-C was determined. A Heraeus Sun-Test chamber, equipped with a xenon arc lamp filtered to yield a simulated solar spectrum, was used for the irradiation. An additional infrared filter minimized sample heating. The irradiance at the sample location was originally 0.83 W/m2 at 340 nm, but the output decreased approximately 20% after 1500 hours use. Long band-pass optical filters with nominal cut-offs of 305 nm, 345 nm, 385 nm and 400 nm were inserted between the xenon lamp and the Parylene-C film samples to determine the wavelength threshold for yellowing. The sample temperature was maintained at 30+ 2 °C with a water-cooled... 

Fig. 6.12 The transmission spectrum for a band-pass optical filter.

The basic function of band-pass optical filters is to efficiently transmit light within a chosen wavelength band and effectively reject the wavelengths lying outside of this band. The ratio of the in-band (desired) transmitted energy to the out-of-band (undesired) transmitted energy is the single most important parameter to be considered. 

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