Development of 10 μm~11 μm bandpass filter for surface temperature detection

The multispectral spectral imager equipped with a long-wave infrared detector can provide spatially high-resolution surface temperature information, and the study of surface temperature is of great significance in the global energy balance and climate change. A 10 μm~11 μm filter was used as the window of the infrared detector for surface temperature detection, and a wide-cutoff and high-transmission long-wave infrared bandpass filter film was designed on a Ge substrate using Ge and ZnS as the high and low refractive index materials, respectively. Vacuum coating technology was used to prepare long-wavelength pass and short-wavelength pass filter films on both sides of the Ge plate to realize the bandpass, in which Ge and ZnS films were deposited by electron beam and resistive thermal evaporation, respectively, and the film thickness was controlled by a crystal controller. The mathematical model of film thickness deposition was established by Matlab software, which simulated and corrected the tooling of the multilayered film in order to reduce the thickness error. The test results show that the average transmittance of 10 μm~11 μm reaches 94.3%, and the ripple amplitude of the transmittance area is 1.6%, of which the average transmittance of 4 μm~9.5 μm and 11.5 μm~16 μm is less than 0.1%, and the filter meets the requirements of the use through various environmental tests.