A summary of recent damage-initiation experiments on KDP crystals

Abstract

We summarize recent investigations of the density and morphology of bulk damage in KDP crystals as a function of pulse duration, temporal profile, wavelength, and energy fluence. As previously reported by Runkel et al. 1, we also find that the size of bulk damage sites varies roughly linearly with pulse duration for pulses between 1 ns and 9 ns. However this trend no longer applies at pulse durations below 1 ns. Experiments measuring the damage density and size distribution as a function of wavelength confirm many previous works which indicated a strong dependence of damage density with wavelength. However, we also find that the size of damage sites is relatively insensitive to wavelength. Further we see damage due to Flat-In-Time (FIT) pulses has different pulse length and fluence dependence than Gaussian pulses. We demonstrate that a simple thermal diffusion model can account for observed differences in damage densities due to square and Gaussian temporally shaped pulses of equal fluence. Moreover, we show that the key laser parameter governing size of the bulk damage sites is the length of time the pulse remains above a specific intensity. The different dependences of damage density and damage site size on laser parameters suggest different absorption mechanisms early and late in the damaging pulse.

Influence of Light Intensification by Subsurface Cracks on KH2PO4Crystal's Laser Induced Damage Threshold

“…Namely that the crystal tends to collapse more easily when exposed to laser with short wavelength, and this phenomenon has been proved by the results of many experiments. [24][25][26] Figure 3(a) shows that the maximum light intensity inside KDP crystal can be about 4-7 times of the ideal light intensity, namely that the practical LIDT will decrease to around 14-25% of the ideal LIDT when just considering the modulation effect of subsurface crack. If the non-linear absorption effect at the hot spots is considered, the drop of LIDT will be more conspicuous.…”

Development of a KDP crystal growth system based on TRM and characterization of the grown crystals

“…Study of damage laser threshold is an important parameter in qualification of nonlinear crystals [12]. In our experiment measurements were performed according to international standard ISO 11254 using a Nd:YAG laser vertically irradiated on the surface of sample with wavelength of 1064 nm in TEM 00 transverse mode by linear polarization.…”