26 February 2015 Diagnostics of pulse contrast for petawatt laser in SGII
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Abstract
Pulse contrast is an important parameter for ultrafast pulses. It shall be 108 or higher in order to avoid effect from noise before main pulse. Diagnostics with cross-correlation can achieve high temporal resolution such as ~7fs. Cross-correlation has advantage in pulse contrast measurement than autocorrelation because it can distinguish noise before or after main pulse. High dynamic range is also essential in pulse contrast measurement. Cross-correlation signal from a single shot is converted into a signal series through fiber array, which can be analyzed by a set of a PMT and an oscilloscope. Noise from nonlinear crystal and scatter needs decrease to improve dynamic range. And pulse power is also discussed in pulse contrast experiments. Time delay τ is generated by travel stage in measurement for repetition pulses. Then energy instability will generate error in this measurement. In measurement for single shot pulse, time delay τ is generated by slant angle of beams. The scanning procession is completed with thousands parts of beam section within a single shot, and error will generated from no uniformity in near field. Performance test of pulse contrast measurement is introduced in subsequent sections. Temporal resolution is testified by self-calibration. Dynamic range is judged by a parallel flat. At last pulse contrast of petawatt laser is diagnosed by a single shot cross-correlator with high confidence. The ratio is 10-6 at 50ps before main pulse, and 10-4 at 10ps before main pulse.
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Xiaoping Ouyang, Daizhong Liu, Baoqiang Zhu, Jian Zhu, Jianqiang Zhu, "Diagnostics of pulse contrast for petawatt laser in SGII", Proc. SPIE 9345, High Power Lasers for Fusion Research III, 93450R (26 February 2015); doi: 10.1117/12.2178692; https://doi.org/10.1117/12.2178692
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