Rong Qiu

The size prediction of potential inclusions embedded in the sub-surface of fused silica by damage morphology

Abstract A model for predicting the size ranges of different potential inclusions initiating damage on the surface of fused silica has been presented. This accounts for the heating of nanometric inclusions whose absorptivity is described based on Mie Theory. The depth profile of impurities has been measured by ICP-OES. By the measured temporal pulse profile on the surface of fused silica, the temperature and thermal stress has been calculated. Furthermore, considering the limit conditions of temperature and thermal stress strength for different damage morphologies, the size range of potential inclusions for fused silica is discussed.

Initiated damage of laser induced in fused silica at 1064nm and 532nm

The useful lifetime of a laser optic in high power laser system is limited by both laser-induced initiated damage and the subsequent growth. We have studied and measured the initiated damage morphology on fused silica surface in air at 1064nm and 532nm at nanosecond. Results demonstrate a significant dependence of the initiated damage morphology and size on the type, diameter and lodging depth of the surface defects. We will compare the initiated damage morphology for entrance- and exit-surface. Possible reasons for the observed initiated damage behavior are discussed.

Investigation on Laser Damage Probability of Fused Silica with Simultaneous Multi-wavelength Irradiation

The surface damage performance of fused silica under mono-wavelength configuration or simultaneous dual-wavelength exposures to 1053, 527, and 351xa0nm nanosecond-laser pulses is investigated in order to probe the mechanisms governing damage initiation during frequency conversion. Based on the absorption and heat transfer mechanism, coupled to laser damage statistics, a model considering the Gaussian distribution of irradiation intensity has been presented to obtain precise calculation result about laser damage probability. Laser damage probability curves are measured on the surface of fused silica with different wavelength configurations. By studying the influence of the laser wavelength configurations on the laser damage probability, we show with our methodology that the types of damage precursors under the irradiation of different wavelength configurations can be identified.

Influence of secondary treatment with CO2 laser irradiation for mitigation site on fused silica surface

The ablation debris and raised rim, as well as residual stress and deep crater will be formed during the mitigation of damage site with a CO2 laser irradiation on fused silica surface, which greatly affects the laser damage resistance of optics. In this study, the experimental study combined with numerical simulation is utilized to investigate the effect of the secondary treatment on a mitigated site by CO2 laser irradiation. The results indicate that the ablation debris and the raised rim can be completely eliminated and the depth of crater can be reduced. Notable results show that the residual stress of the mitigation site after treatment will reduce two-thirds of the original stress. Finally, the elimination and the controlling mechanism of secondary treatment on the debris and raised rim, as well as the reasons for changing the profile and stress are analyzed. The results can provide a reference for the optimization treatment of mitigation sites by CO2 laser secondary treatment.

Comparison of bare and sol-gel coated of mitigated site on fused silica

The performance of mitigated site coated with antireflective (AR) coating is investigated, and its discrepancy is also investigated by comparing the bare site with substrate from surface morphology and profile, transmittance and laser induced damage threshold (LIDT). The results indicated that more SiO2 sol will be deposited in the crater of mitigated site during the dipping process, while the coated site does not seriously influence the performance of the entire sample. The LIDT results indicate that both the coated substrate and mitigated site are lower than that of un-coated substrate and mitigated site. Keywords: fused silica; mitigated site; coating; sol-gel.