Windows and lenses used in the UCSB optical transport system are made of TPX (polymethylpentene). This is a high temperature (200° C) copolymer made by Mitsui & Co Ltd., Japan - petrochemical div. Its most important property is optical transparency in both the far-infrared and visible parts of the spectrum, allowing the co-transmission of a HeNe laser alignment beam. Index of refraction is 1.46 and is relatively independent of wavelength. Loss is very low at mm-wavelengths and gradually increases until becoming unacceptable in the mid-IR at about 30 to 50 microns wavelength.
The windows and lenses are turned on a template guided lathe, then hand polished. There are no unusual problems with either machining or polishing.
Our material was purchased as a large 1 inch thick sheet in 1988 from Port Plastics in Los Angeles. It is no longer available from that source, and ours is essentially used up. The following is a list of potential suppliers: