Far Infrared Isolator.

It has been determined that optical isolators for linearly polarized laser beams of moderate power may be constructed with n-type InSb as the active element. The effect used in the device is the difference between the large free electron Faraday effect and the somewhat smaller interband Faraday effect. Somewhat unexpectedly, the authors find that the magnitude of the Faraday effect varies greatly with crystal orientation and absorption coefficients differ with suppliers of the crystals. In a typical device, the InSb wafer is about 0.38 mm thick, is maintained at liquid nitrogen temperature, has a donor Te concentration of about 3 x 10 to the 17th powercc and provides 45 degrees rotation in a field of about 3500 Gauss. The dissipated power is less than 20 of the incident and there is no danger of thermal runaway for power densities up to 500 wattssqcm. The quality of the isolation depends primarily on the quality of the analyzers used. Author