MULTILAYER INTERFERENCE FILTERS FOR THE FAR-INFRARED AND SUBMILLIMETER REGIONS

The theoretical and experimental aspects of an alternative approach to the construction of interference filters for wavelengths greater than 80 mum are described. The filters consist of a number of thin plastic sheets with films of a high refractive index deposited onto one or bo th sides of each sheet. These are then heat bonded to form a self-supp orting optical multilayer filter. Experimental results are presented f or a number of filters produced in this way. Reflectances of the order of 90% have been measured for wavelengths as high as approximately 20 0 mum. By successive reflections from two or more such multilayers it is possible to produce efficient, narrow-bandpass filters with blockin g over extended spectral regions. The possibility of the construction of other devices, including even narrower bandpass filters and wideban d beam splitters, is also discussed.