Thermal stress cleaving of glass-based X-ray telescope lenses by heated wire to eliminate microdefects

Abstract

Abstract The satellite borne X-ray telescope (XRT) is a key technical tool for studying major astronomical problems in the universe. During the fabrication of ultra-thin glass lenses for XRTs, conventional glass cutting technologies yield micro-cracks along the cut surface or micro-damage on the surfaces of the glass normal to the cut. These micro-defects will cause the lenses to be damaged by the strong vibration and jerk of the launch process. In this paper, we seek to resolve this issue by developing a non-destructive cutting technique for glass lenses. Specifically, in this study we propose a heated wire thermal stress cleaving method. We derived the principal parameters affecting the thermal stress fracture behavior of lenses and furthermore calculated the relationship between the length of the initial crack and the minimum temperature. Experimental studies are performed to investigate the process parameters that affect the propagation of a crack in the telescope lens during the thermal stress cleaving process. In particular, we have successfully achieved thermal stress cleaving of a 0.3mm thick lenses with a surface roughness Ra of less than 0.5nm. When assessed in a satellite launch vibration test with a maximum accelerations amplitudes of 5g and 6g in the Y- and Z-directions, respectively, no crack propagation or damage was observed on the surface of the obtained telescope lenses. The study lays a foundation for the manufacture of glass-based XRT.