Thermal optical analysis of optical window glass

Abstract

Optical window is a multifunction window. It is not only a window that let the light come through, it is also a window, which isolate the vacuum environment inside the bottle from the outside atmosphere environment. At the same time, it is as well as a temperature-controlling window that can separate the heat sink inside the bottle away from the outside normal temperature. The thickness of the glass should be large enough to guarantee the strength and reliability of the window. But if the window glass is too thick, it would lead to the temperature change and, furthermore, would cause to the change of refractive index gradient and also, the thermal deformation will be more apparent. It may even be able to meet the requirements of the optical indicator when the situation gets worse. Based on the thermal optical analysis, with one side in normal pressure, and the other in 1 ☓ 10−3 Pa vacuum, 100 K degrees, the thickness of the silica glass and the germanium optical window is optimized. The thermal environment of optical window is analyzed, including system average temperature shift as well as circumferential, radial and axial temperature differences. By calculate the result of steady state temperature field and mapping it to structural model, the deformation of optical window under the force-thermal coupling condition could be figured out. The thermal optical analysis could also be carried out after combining refractive index gradient analysis and glass surface change of optical window. With the differences of glass thickness, the optical path in root mean square error (RMS) of silica glass optical window with diameter of 230 mm and the germanium optical window with diameter of 150 mm is calculated. The results show that the optical window can not only meet the strength and reliability requirements, but also meet the optic index in the effective optical aperture. These results provide the guidance for the optical window design.