Closed cycle cryogenic refrigerators as integrated cold sources for infrared detectors.

Many ir detectors can only operate when cooled to low temperatures. A short description is given of an integrated refrigerator-detector combination in airborne use. Experimental results are presented for developmental refrigerators in which weight and power input have been reduced to a point where satellite- borne operation becomes feasible.

Effective thickness of bulk materials and of thin films for internal reflection spectroscopy.

In internal reflection spectroscopy effective thickness is defined as the thickness of material required to give a spectrum of the same contrast in a transmission measurement as that obtained via internal reflection. Simple expressions for effective thickness are given for bulk materials and for thin films which are useful as guide lines in determining the optimum conditions required to record internal reflection spectra. Depending on angle of incidence and index of refraction, the effective thickness for bulk materials may be much greater or much less than the wavelength of light. Similarly for thin films the effective thickness may be much greater or much less than the actual thickness.