The issues of laser-induced damage of transparent dielectric optics severely limit the development of large laser systems. In order to explore the mechanism of nanosecond laser damage on KDP surface, a multi-physics coupling dynamics model and a time resolved detection system were developed to obtain the transient dynamic behaviors of laser damage. The behaviors of laser energy transmission, thermal field distribution and damage morphology during nanosecond laser irradiation on KDP surface were simulated. It is found that the enhancement of light intensity caused by surface defect plays an important role in the initial energy deposition and damage initiation of the laser irradiation area. The evolution of the temperature field and fluid flow during subsequent laser irradiation contributes to the laser damage process. The simulated evolution of heat absorption source is verified by the transient images of local defect-induced laser damage captured by the ultra-fast experimental detection system. This work provides further insights in explaining the laserinduced damage by surface defects on KDP crystals.
White light scanning interferometry (WLSI) is a fast, noncontact, high-precision method to measure three-dimensional (3D) surface profile and extensively used in roughness measurement of ultra-precision machined surface. However, due to Rayleigh criterion, the lateral resolution of WLSI is limited to hundreds of nanometers. It is hard to measure rough surfaces with delicate details that adjacent distance less than lateral resolution. Also, WLSI can’t measure profiles with large surface gradient for no light reflected and received by objective lens. In this work, with a proposed simulation measurement model, surface gradient error and lateral resolution error on measuring result of WLSI is studied by simulating the response characteristics of sinusoidal signal, square signal, sawtooth signal and actual surface profile of grinding silicon wafer measured by AFM respectively. The effectiveness of the simulation model is verified by comparing the simulation results with the experimental results. The mechanism of surface gradient error and lateral resolution error is revealed from the perspective of simulation analysis, which has certain guiding significance for the future research of error analysis on white light scanning interference.
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