An Apparatus for the Directional Spectral Emissivity Measurement in the Near Infrared Band

Abstract

A measurement apparatus based on the optical fiber spectrometer is established to measure the directional spectral emissivity in the near infrared band. The sample is heated by a self-designed silicon carbide heater. The measurement angle can be adjusted from 0° to 82° by rotating the fiber collimating lens installed in a motorized rotary stage. The radiation signals of the sample and blackbody can be detected with a micro-optical fiber spectrometer in real time. The spectral emissivities of silicon wafer, silicon carbide, molybdenum, and tungsten are measured to verify the reproducibility and reliability of the apparatus. Furthermore, the directional spectral emissivity of high-purity chromium is investigated in the wavelength range from 950 nm to 1600 nm and the temperature range from 823 K to 1073 K. The influences of wavelength, temperature, and measurement angle on the spectral emissivity are analyzed in detail. It is found that the directional spectral emissivity of chromium decreases with the increasing wavelength and the temperature. The spectral emissivity of chromium rises slowly and then falls sharply with the increasing measurement angle. The combined uncertainty of emissivity measurement is evaluated, which is no more than 3 % for the wavelength and temperature range considered.