The optical properties of GaAs, GaP, and CVD diamond, which are being developed by Texas Instruments specifically for infrared optics, are continually being improved. The data reported here indicates the current usefulness and directions for further improvement of these materials. Bulk-grown GaAs has been developed that has near-intrinsic absorption coefficients for both high-resistivity (107 ohm-cm) and conductive (<1 ohm-cm) type material. Its transparency extends from 0.9 to 16.0 micrometers . The absorption coefficient at 1.06 micrometers is 0.3 cm-1 for high-resistivity GaAs and 0.5 cm-1 for conductive GaAs. The absorption coefficients for 2 to 12 micrometers are <0.01 cm-1 for high-resistivity GaAs up to nearly 400 degree(s)C and up to nearly 200 degree(s)C for the conductive GaAs. GaP is transparent from 0.6 to 12.0 micrometers . The absorption coefficient at 1.06 micrometers is 0.1 cm -1; from 2 to 7 micrometers , the coefficients are <0.01 cm-1; from 8 to 10 micrometers , they are <0.1 cm-1, except at 9.25, where the coefficient is 0.5 cm-1. Diamond is transparent from 0.2 to 4.0 micrometers and for all wavelengths beyond 5.5 micrometers . Current CVD diamond is limited by light scattering, hydrogen and other impurity absorption, and defect-induced one-phonon absorption. Absorption coefficient values at 8 to 12 micrometers are 1 cm -1 with some peak absorption of a few cm-1.