METAL DIELECTRIC TRANSMISSION INTERFERENCE FILTERS WITH LOW REFLECTANCE .1. DESIGN/

For many applications the high reflectance of conventional multilayer interference filters is undesirable. It is possible to design and cons truct interference filters in which the transmittance and reflectance are independently controlled and in which the reflectance is very low. However, to do this it is necessary to employ absorbing coating mater ials and, as a result, a reduction in the peak transmittance must be a ccepted. We describe three different methods for the design of such co atings. Examples are given of a number of bandpass filters, neutral de nsity filters, cutoff filters, and of an ($) over bar x(lambda) tristi mulus filter, all having a low reflectance. This reflectance is freque ntly 15 to 50 times lower than that of conventional filters.