Implications of nanoabsorber initiators for damage probability curves, pulselength scaling, and laser conditioning

Abstract

Laser damage of large optics initiates at material imperfections. Absorbers of very small, nanoscale size are possible initiators. We will analyze experimental implications of assuming that the damage is initiated by a size distribution of nanoabsorbers. We will demonstrate that the model predicts damage fluence pulselength scaling consistent with experiment. The size distribution of nanoabsorbers is related to the resulting damage site density and to the shape of the damage probability curve (S-curve). Conditioning of KDP crystals can be explained within the same model. The relative efficiency of various conditioning strategies is discussed

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

“…A statistical trend has been observed in damage tests due to size distributions [15][16][17][18][19] (Dirac, power law, Gaussian law) of the inclusions. The damage density and damage probability dependend on laser parameters (fluence, pulse length, spot size, or wavelength) and this has been observed in the experiments [20][21][22].…”

“…Thus, the thermal properties of the surrounding matrix are of critical importance for the temperature rise [15], so the calculation only considers the dependence of thermal properties of the host material on the temperature. In this manuscript, considering the real temporal shape of the laser pulse by fitting a measured Gaussian temporal profile, we refined previous model [20][21][22] to calculate the particle temperature.…”

Transmittance increase after laser conditioning reveals absorption properties variation in DKDP crystals

“…Feit suggested that the increase of LIDT was due to the defect decreasing in size during laser exposure [3]. Chirila believed that electronic structure of the defect was altered during laser exposure [18].…”

“…The observed damage thresholds of KDP/DKDP crystals are much lower than the intrinsic thresholds [2]. It is now admitted that this damage is induced by point defects that efficiently absorb laser energy, inducing a fast temperature rise and a subsequent "micro-explosion" [3][4][5]. In order to ensure a good running of laser system, it is necessary to identify the nature of point defect and to understand the physical mechanism leading to laser damage.…”

“…The point defects corresponding to hydrogen or oxygen atoms as interstitial atoms or vacancies in the crystalline lattice have attracted more and more attentions in recent years. A simple model based on heat transfer [3,8,15] have demonstrated that the point defect size ranges between roughly 10 nm and 100 nm cannot produce a sufficiently high temperature, only a cluster of point defects can satisfy the defect size requirement.…”