Results of applying a non-evaporative mitigation technique to laser-initiated surface damage on fused-silica

Abstract

We present results from a study to determine an acceptable CO 2 laser-based non-evaporative mitigation protocol for use on surface damage sites in fused-silica optics. A promising protocol is identified and evaluated on a set of surface damage sites created under ICF-type laser conditions. Mitigation protocol acceptability criteria for damage re-initiation and growth, downstream intensification, and residual stress are discussed. In previous work [1], we found that a power ramp at the end of the protocol effectively minimizes the residual stress (<25 MPa) left in the substrate. However, the biggest difficulty in determining an acceptable protocol was balancing between low re-initiation and problematic downstream intensification. Typical growing surface damage sites mitigated with a candidate CO 2 laser-based mitigation protocol all survived 351 nm, 5 ns damage testing to fluences >12.5 J/cm 2 . The downstream intensification arising from the mitigated sites is evaluated, and all but one of the sites has 100% passing downstream damage expectation values. We demonstrate, for the first time, a successful non-evaporative 10.6 m CO 2 laser mitigation protocol applicable to fused-silica optics used on fusion-class lasers like the National Ignition Facility (NIF).

Densification and residual stress induced by CO 2 laser-based mitigation of SiO 2 surfaces

“…Such densification also results in residual stress. The practical importance of choosing cooling programs to reduce such stresses in described 14 in an accompanying paper in these proceedings.…”

Imaging of Phase Objects using Partially Coherent Illumination

“…Failing flaws can be reworked to mitigate their fratricide threat before installing the optic, either by applying a physical mitigation protocol [16][17][18] to the flaw itself, or by spot blocking [19] that location in the laser system before firing a high-power shot.…”

Full Aperture CO2Laser Process to Improve Laser Damage Resistance of Fused Silica Optical Surface

“…For the fused silica optics, lots of researches indicate that carbon dioxide (CO 2 ) laser treatment is an effective mean to mitigate the problem of laser damage. One of the most common ways is to mitigate the damage site by melting or evaporation, thus avoiding their catastrophic growth under subsequent laser irradiation [5,6]. But as early as 1979, Temple et al [7] had proposed an idea to polish fused silica optics by CO 2 laser for improving the damage resistance at 1064 nm.…”