Apparent temperature verses true temperature of silicon crystals as a function of their thickness using infrared measurements

Abstract

Viewing the surface of objects subjected to high heat fluxes with an infrared camera or infrared sensor has proven to be a very effective method for monitoring the magnitude and distribution of surface temperatures on an object. This approach has been quite useful in studies of cooling silicon crystals in monochromators subject to high heat loads. The main drawback is that single crystals of silicon are partially transparent to infrared radiation as monitored in most infrared cameras. This means that the infrared radiation emitted from the surface contains a component that comes from the interior of the crystal, and that the intensity of the emitted radiation and thus the apparent temperature of the surface of the crystal depends on the thickness of the crystal and the kind of coating on the back (and/or the front) of the crystal. The apparent temperature of the crystal increases as the crystal is made thicker. A series of experiments was performed at Argonne National Laboratory to calibrate the apparent temperature of the crystal as measured with an infrared camera as a function of the crystal thickness 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 temperature of the crystal and simulates the response of a crystal twice the thickness. These measurements make it possible to interpret infrared signals from cooled silicon crystals used in earlier high-heat-load experiments. A number of examples are given for data taken in synchrotron experiments with high intensity X-ray beams.