title: Investigation of stress induced by CO2 laser processing of fused silica optics for laser damage growth mitigation.
abstract: Laser damage mitigation' is a process developed to prevent the growth of nanosecond laser-initiated damage sites under successive irradiation. It consists of re-fusing the damage area with a CO2 laser. In this paper we investigate the stress field created around mitigated sites which could have an influence on the efficiency of the process. A numerical model of CO2 laser interaction with fused silica is developed. It takes into account laser energy absorption, heat transfer, thermally induced stress and birefringence. Residual stress near mitigated sites in fused silica samples is characterized with specific photoelastic methods and theoretical data are compared to experiments. The stress distribution and quantitative values of stress levels are obtained for sites treated with the CO2 laser in various conditions of energy deposition (beam size, pulse duration, incident power). The results provided evidence that the presence of birefringence/residual stress around the mitigated sites has an effect on their laser damage resistance.
authors.affiliation: Institut Fresnel, CNRS, Aix-Marseille Université, Ecole Centrale Marseille, Campus de Saint-Jérôme, 13013 Marseille, France. laurent.gallais@fresnel.fr
authors.forename: Laurent
authors.initials: L
authors.lastname: Gallais
authors.forename: Philippe
authors.initials: P
authors.lastname: Cormont
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Rullier
mesh_terms: D004307:Dose-Response Relationship, Radiation; D054020:Lasers, Gas; D011829:Radiation Dosage; D012822:Silicon Dioxide / Q000737:chemistry* / Q000528:radiation effects*; D013314:Stress, Mechanical; D013499:Surface Properties / Q000528:radiation effects
chemical_list: D012822:Silicon Dioxide