LASER INTERFEROMETRIC THERMOMETRY FOR SUBSTRATE-TEMPERATURE MEASUREMENT

This paper investigates a simple noncontact optical thermometry technique based on the laser interferometric measurement of the thermal expansion and refractive index change of a thin transparent substrate or temperature sensor. The technique is shown to be extendible from room temperature to at least 900-degrees-C with the proper choice of a thermally stable sensor. Sensor materials investigated included c-axis Al2O3, MgO, MgAl2O4 (spinel), Y2O3-ZrO2 (yttria stabilized zirconia), and fused silica. Calibration data were taken at 633 nm by measuring the sensor response to known temperature changes. These data provided (1) the information needed for quantitative thermometry (i.e., the functional relationship between interference fringes and temperature for samples of known thickness) and (2) the thermal coefficient of refractive index for those materials with known thermal expansion coefficients.