ULTRA-NARROW BANDPASS INTERFERENCE FILTER FOR INFRARED APPLICATION

ABSTRACT In this work, a theoretical designs of ultra-narrow bandpassfilter to operate in the infrared region ( i. e. for laser CO2 ) is proposed, in order to detect spectral lines with full width at half maximum (FWHM) is less than 2 nm. This filter is constructed by coat substrate by two transparent coating material with high and low refractive index. The effect of incidence angle of the electromagnetic on the filter also studied. The results shows that, for normal incidence, high transmittance ( T ? 98 % ) at the center of design wavelength(λo) with very lowtransmittance in the rejection region. As the angle of incidence increase, the transmittance decreases as a result of varying in thickness of the layers.