Comparing the use of 4.6μm lasers versus 10.6 μm lasers for mitigating damage site growth on fused silica surfaces

摘要

The advantage of using mid-infrared (IR) 4.6 μm lasers, versus far-infrared 10.6 μm lasers, for mitigating damage growth on fused silica is investigated. In contrast to fused silica's high absorption at 10.6 μm, silica absorption at 4.6 μm is two orders of magnitude less. The much reduced absorption at 4.6 μm enables deep heat penetration into fused silica when it is heated using the mid-IR laser, which in turn leads to more effective mitigation of damage sites with deep cracks. The advantage of using mid-IR versus far-IR laser for damage growth mitigation under non-evaporative condition is quantified by defining a figure of merit (FOM) that relates the crack healing depth to laser power required. Based on our FOM, we show that for damage cracks up to at least 500 μm in depth, mitigation using a 4.6 μm mid-IR laser is more efficient than mitigation using a 10.6 μm far-IR laser.