Measurement of weak absorption in optical thin films.

An adiabatic laser calorimeter for measuring weak absorption in optical thin films is presented. It consists of three main parts which are used to control and measure temperature, and for calibration. The controlling temperature part is a set of automatic temperature controls mainly composed of a PID adjuster. The temperature difference between specimen and environment is always less than +/-0.006 degrees C during the measurement process. There is almost no energy exchange between specimen and environment. The specimen temperature increment is measured by a high precision thermistor set. Its measuring temperature sensitivity is 0.003 degrees C and the accuracy is +/-0.004 degrees C. The absolute electrical calibration part is used to obtain absorptance of a specimen immediately without needing to know the mass and specific heat of the specimen. Absorptance as small as 1 x10(-5) can be detected when a 1.5-W argon-ion laser is used.