Quantitative measurement of CO₂laser-induced residual stress in fused silica optics

Abstract

Abstract. The residual stress field of fused silica induced by continuous wave CO 2 laser irradiation is investigated with specific photoelastic methods. Both hoop stress and axial stress in the irradiated zone are measured quantitatively. For the hoop stress along the radial direction, the maximum phase retardance of 30 nm appears at the boundary of the laser distorted zone (680-μm distance to center), and the phase retardance decreases rapidly and linearly inward, and decreases slowly and exponentially outward. For the axial stress, tensile stress lies in a thin surface layer (<280 μm) and compressive stress lies just below the tensile region. Both tensile and compressive stresses increase first and then decrease along the depth direction. The maximum phase retardance induced by axial tensile stress is 150 nm, and the maximum phase retardance caused by axial compression stress is about 75 nm. In addition, the relationship between the maximum axial stress and the deformation height of the laser irradiated zone is also discussed.

Residual stress modeling of mitigated fused silica damage sites with CO2 laser annealing

“…The radial characteristic shape of the optical retardance for quench-cooled mitigated damage sites is in agreement with the reported measurement. [23] CO 2 laser annealing can effectively reduce the optical retardance of mitigated damage sites. The slope of the radial optical retardance profile of the laser-annealed mitigated damage sites dramatically decreases compared with that of quench-cooled mitigated damage sites.…”