The current research demonstrates the effectiveness ofboth silicon and germanium as transmissive materials for use within the far infrared wavelength range of2O to 160 microns. This study involves samples with a wide range ofresistivities and temperatures including: n-type Si of4000, 2000, 160, 65, 12, and 2.6 ohm-cm and p-type Si of 500 and 60 ohm-cm within a temperature range of -100°C to 250°C and n-type Ge of39, 25, 14.5, 5.0, 2.5, and 0.5 ohm-cm within a temperature range of-100°C to 100°C. Far infrared absorption mechanisms are briefly discussed. The experimental absorption data are used to discuss the interaction between absorption by lattice resonance and free carrier absorption. Highly resistive germanium and silicon are both found to be excellent transmissive materials in the far infrared. These studies may be used to develop the feasibility of silicon and germanium as optical windows or lenses within an extraterrestrial environment.

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Both silicon and germanium are widely used as transmissive elements in the infrared region ofthe spectrum. Both materials are typically used in applications where significant temperature ranges exist. In this work we report transmission in the wavelength range of 1.39 to 22 un and in the temperature range ofroom temperature (25°C) down to -100°C for silicon and germanium samples of various resistivities. The data presented indicate an orderly change in transmission with decreasing temperature for the various sample resistivities. Absorption coefficients are calculated from the transmission data.