An effective damage test method based on a marker-based watershed algorithm with gray control (MWGC) is proposed to study the properties of damage induced by near-field laser irradiation for large-aperture laser facilities. Damage tests were performed on fused silica samples and information on the size of damage sites was obtained by this new algorithm, which can effectively suppress the issue of over-segmentation of images resulting from non-uniform illumination in darkfield imaging. Experimental analysis and results show that the lateral damage growth on the exit surface is exponential, and the number of damage sites decreases sharply with damage site size in the damage site distribution statistics. The average damage growth coefficients fitted according to the experimental results for Corning-7980 and Heraeus-Suprasil 312 samples at 351 nm are 1.10 ± 0.31 and 0.60 ± 0.09, respectively.
A single-shot measuring apparatus with optical limiting for temporal pulse contrast of
kJ-class petawatt lasers in the nanosecond range is proposed. A
temporal linear filter comprising an electro-optical switch, a
polarizer, a temporal nonlinear filter composed of cascaded SHG
crystals, and a dichromatic mirror are, respectively, used as an
optical limiting apparatus for contrast measurement of nanosecond and
picosecond pulses to improve dynamic range and temporal resolution.
The apparatus has been applied to pulse contrast measurements at the
SG-II petawatt facility, achieving a high dynamic range of
1
0
10
and a fast time resolution of 107 ps
in the 350 ns range. This technique can also be universally applied to
the limiting of the main pulse of varying pulse widths to diagnose
pre-pulses during generation and transmission.
A high-energy, high-beam-quality, and pulse-width-tunable Nd:YAG laser system, pumped by vertical cavity surface emitting laser arrays and laser diodes, is demonstrated and applied to a velocity interferometry system for any reflector (VISAR) application in a high power laser facility. A multistage multipass amplification structure is used to fully extract the amplifier energy and obtain a high-energy pulse. The temporal waveform is compensated to provide a square waveform, with a flatness less than 8% (peak-to-peak value). The peak power is greater than 100 kW with a frequency-doubling efficiency of 25% for a 50 ns pulse width. The laser operates as a single shot with 1–5 Hz repetition frequency and 0.7% rms energy stability.
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