Dynamic measurement of reflectance/emissivity in mid-infrared band

摘要

In order to measure the change of laser energy coupling coefficient with temperature in mid-infrared wave band, reflectance integrating sphere experiment system was designed and set up. 915nm CW laser was used to heat samples and the wavelength of probe laser is 3.8μm. Chopper and phase-locked amplifier were adopted in the system. Thermal imager was used to measure and record the temperature of samples during laser irradiation. The reflectance of steel and aluminum plates to 3.8μm was measured during 915nm laser irradiation. EDS analysis was done to investigate the change of elemental composition in the samples respectively. The experimental results show that, the results of reflectance and radiation temperature measured by this system are relatively accurate during laser irradiation. In the process of temperature rising from 300K to 785K, the color of 45# steel plates turns blue and black, while the color of aluminum alloy plates is basically unchanged. When temperature reaches about 700K, reflectance of 45# steel decreases obviously with the increase of temperature, while reflectance of aluminum is almost constant. The reflectance is probably determined by the oxide in the surface of samples which is consistent with the results of EDS analysis. Reflectance decreases with the increase of the content of oxygen in the surface. The reason of why the reflectance of aluminum is almost constant is that aluminum oxide is not generate massively under 750K.