Far infrared transmission filters for the 300-18 cm (-1) spectral region

Emissivity measurements of reflective surfaces at near-millimeter wavelengths

We have developed an instrument for directly measuring the emissivity of reflective surfaces at near-millimeter wavelengths. The thermal emission of a test sample is compared with that of a reference surface, allowing the emissivity of the sample to be determined without heating. The emissivity of the reference surface is determined by one's heating the reference surface and measuring the increase in emission. The instrument has an absolute accuracy of Δε = 5 × 10(-4) and can reproducibly measure a difference in emissivity as small as Δε = 10(-4) between flat reflective samples. We have used the instrument to measure the emissivity of metal films evaporated on glass and carbon fiber-reinforced plastic composite surfaces. We measure an emissivity of (2.15 ± 0.4) × 10(-3) for gold evaporated on glass and (2.65 ± 0.5) × 10(-3) for aluminum evaporated on carbon fiber-reinforced plastic composite.

Far-infrared high-resolution Fourier transform spectrometer: applications to H(2)O, NH(3), and NO(2) lines

A Michelson-type Fourier transform spectrometer has been constructed for high resolution work in the far ir. The instrument has a theoretical resolution of 0.007 cm(-1) and can be used with a tunable band pass filter system for the reduction of sampling points in a specific spectral region. Separations of 0.05 cm(-1) in the inversion spectrum of NH(3) in the 200-cm(-1) spectral region have been observed with about 1000 sampling points and splittings of 0.04 cm(-1) in the NO(2) spectrum at about 100 cm(-1).

Far infrared interference filters

Capacitive meshes for far ir, low pass filters are prepared from Cu layers on 2.5 micro plastic film. The properties of these meshes of different mesh constants g with their different combinations in two-mesh, fourmesh, and eight-mesh filters are studied in the spectral region 160 cm(-1) to 10 cm(-1) by the use of a grating spectrometer. The applications of these meshes as low pass filters in the far ir spectral region in a grating spectrometer are described.