APPARENT TEMPERATURE VERSES TRUE TEMPERATURE OF SILICON-CRYSTALS AS AFUNCTION OF THEIR THICKNESS USING INFRARED MEASUREMENTS

Viewing the surface of objects subjected to high heat fluxes with an i nfrared camera or infrared sensor has proven to be a very effective me thod for monitoring the magnitude and distribution of surface temperat ures On an object. This approach has been quite useful in studies of c ooling silicon crystals in monochromators subject to high heat loads. The main drawback is that single crystals of silicon are partially tra nsparent to infrared radiation as monitored in most infrared cameras. This means that the infrared radiation emitted from the surface contai ns a component that comes from the interior of the crystal, and that t he intensity of the emitted radiation and thus the apparent temperatur e of the surface of the crystal depends on the thickness of the crysta l and the kind of coating on the back (and/or the front) of the crysta l. The apparent temperature of the crystal increases as the crystal is made thicker. A series of experiments was performed at Argonne Nation al Laboratory to calibrate the apparent temperature of the crystal as measured with an infrared camera as a function of the crystal thicknes s and the type of coating (if any) on the back of the crystal. A good reflecting surface on the back of the crystal increases the apparent t emperature of the crystal and simulates the response of a crystal twic e the thickness. These measurements make it possible to interpret infr ared signals from cooled silicon crystals used in earlier high-heat-lo ad experiments. A number of examples are given for data taken in synch rotron experiments with high intensity X-ray beams.