Effects of annealing parameters on transmission wavefront and damage threshold of fused silica

Thermal annealing at high temperature is used to relieve the residual stress of fused silica induced by CO2 laser repair. The effects of annealing environment on surface contamination of fused silica as well as the effects of different annealing temperatures(600 to 900 degree C) and time(3 to 10 h) on residual stress, transmission wavefront,surface roughness, and laser induced damage threshold(LIDT) are investigated. The results show that the residual stress induced by CO2 laser repair can be effectively relieved after annealing at 800 degree C for 10 h and there is no obvious change in the wavefront and surface roughness of optics. A silica shield box can reduce surface contamination from annealing environment but there are still some contaminations undetectable for X-ray photoelectron spectroscopy, which result in a decreased LIDT after annealing. The LIDT can be recovered by HF etching (mass fraction is 1%) for 15 min after annealing and the wavefront and surface roughness of optics do not increase distinctly. (authors)