Changes in optical thicknesses of Ge and SiO thin films and spectral characteristics of narrowband filters at cryogenic temperatures

Abstract

Subject of study. Two narrowband filters with Ge and SiO resonant layers were investigated both at room and cryogenic temperatures of 293 and 80 K, respectively. Aim of study. The deposition of bandpass filters with predefined deviations of optical thickness layers under operating conditions at cryogenic temperatures was considered. The presented design of an optical interference coating increases the transmission coefficient in the operating spectral ranges during its operation at cryogenic temperatures. Method. An antireflective bandpass coating constituting a pair of Ge-SiO film-forming materials was deposited onto a substrate made of an optical material using vacuum deposition. The layer thicknesses were controlled during their deposition using an optical control system. Main results. The obtained spectral characteristics of two narrowband filters are presented herein. The optical thicknesses of the filters with resonant layers made of Ge and SiO and thickness variations at the temperatures of 293 and 80 K were determined by an iteration method via the positions of the wavelengths of maximum transmission of the filters. Practical significance. The spectral characteristics of the filters with SiO resonant layers demonstrated smaller changes at cryogenic temperatures than those of the filters with Ge resonant layers.