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Abstract

A variable temperature dewar has been designed and built at the solid state laboratory of the University of British Columbia for infra-red absorption experiments at low temperatures. The dewar features a rotatable sample holder which brings any one of three samples into the light beam for comparison measurements. A removable tail section permits easy access to the samples. The dewar has been successfully operated over the 4°K to 50°K range. It can maintain sample temperatures to within 1°K for periods up to two hours. Approximately ten minutes is required to achieve any desired temperature in the operating range. The construction and calibration of a copper vs. constantan thermocouple is described. The thermocouple was used to measure the sample temperatures to an accuracy of about 1°K. Temperature variations of a few tenths of a degree could be detected. As a demonstration of the dewar's capabilities, an experiment was performed to measure the line width dependence of hole transitions from the ground state of the P3/2 band to the first excited state in the P1/2 band in boron doped silicon. The experiment showed that the line broadening starts at about 20°K and increases at higher temperatures. Several methods of improving the performance of the dewar are suggested.