The fractional transmission of far infrared radiation through metal light pipes is calculated and compared with experimental data. Transmission factors greater than fifty percent are obtained over distances of several feet with typical parameters. Condensing cones allow the output radiation to be concentrated onto a small detector area for spectroscopic applications.
R. C. OHLMANN, P. L. RICHARDS, and M. TINKHAM, "Far Infrared Transmission through Metal Light Pipes," J. Opt. Soc. Am. 48, 531-532 (1958)