A. Whatley

Far infrared filters for the GALILEO-Jupiter and other missions

Extrapolation of PbTe/II-VI multilayer interference-filter technique from 20 to beyond 40 microm is described and PbTe transparency reviewed; improvements below 20 microm are reported. A composite filter cutting on steeply at 40 microm is described that uses absorptive films of ZnS and As(2)S(3), thin quartz, and supplementary multilayer interference. Absorptive filters are described containing the II-VI compounds since these are found transparent at wavelengths shorter and longer than their reststrahl.

Filters for ν 2 band of CO 2 : monitoring and control of layer deposition

Two types of multilayer interference filter are required for temperature sounding the earths atmosphere. In relation to the 668-cm(-1) nu(2) band of CO(2) these are narrowband (4 cm(-1) wide for the Q branch, 10 cm(-1) for the R branch) or isolation (~60 cm(-1) wide for the complete center of the band). Difficulty in manufacturing the filters for NIMBUS-SCR and -PMR spaceflight has indicated a need for improvement in the monitoring and control of the deposition of layers, and the paper describes a realization of this. The consequent effect on filter performance (utilizing a particular combination of layer materials) is described.

Temperature-Invariant And Other Narrow-Band IR Filters Containing PbTe, 4-20μm

PbTe is unique amongst coating materials because of its negative temperature coefficient of refractive index. In combination with a conventional II-VII) material it can confer immunity to temperature variation from at least -23oC to +110oC for a narrowband filter. It also has an absolutely large refractive index so that filters are attainable with minimal degradation when tilted, and a minimum number of layers overall particularly towards 20 µm. Excellent transmission can be obtained.

Spectrophotometer-type filters of highest possible performance, 2.5–40 μm

Abstract The conceptual design and manufacture of order-sorting spectrophotometer filters are described as cutting on, for example, at 13 and 22 μm:PbTe and ZnS or CdSe layers are used and a CdTe substrate is indicated to eliminate absorption at 16–22 μm. Performance is assessed for a filter of ultimate steepness and transmission, the blocked transmission being below 10 −4 .

Measurement Of Infrared Multilayer Filters At Temperatures Down To 4 Deg K

Measurement is reported at 4 deg K (and blocked transmittance below 10-5) of PbTe/ZnS thin-film filters deposited on Ge substrates. The reduced carrier-absorption which is obtained by cooling these PbTe films is found to accord with simple theory. Advantage for various high-performance multilayers by cooling is significant at the longer wavelengths, and has been verified.

Cooled Filters 16-42 μm Wavelength For FIR Astronomy

The design and manufacture of dielectric-film interference filters for cooled. FIR astronomy is described. The bands are 16.5-21.5 μm, 17.5-19.5 μm, 19.5-21.5 μm and 27 μm cut on. The films are PbTe/CdSe and the substrates are CdTe (some 12 mm thick), without absorption in the region: KRS-6 films are used for antireflection.

Physical Effects In IR-coating Materials

The effects of dispersion, angle of illumination and temperature in coated layers of infrared semiconductors (the IV-VI) and semiinsulators (the II-VI) are described. Examples are given of microcomputer calculations of these.