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Scientists single out how "noise" interferes with the "signal" in Shenguang-II
Update time: 01-21-2019
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    High power laser driver is an important part of an inertial confinement fusion (ICF) laser system, composed of front end, preamplifier, main-amplifier, target, and other control and diagnostic system. As an injection laser system, a nanosecond laser pulse of the front end should possess certain features, such as smooth time envelope, high contrast, and good beam quality. 
    Recently, a research team, led by Professor FAN wei from National Laboratory on High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences, have accurately measured and analyzed in detail the temporal contrast levels of laser pulse in the injection laser system of Shenguang-II facility. 
    In their experiment, they found these signal-to-noise ratio (SNR) levels were determined by the extinction ratios of an acousto-optic modulator, an electro-optic intensity modulator, and a combination of pockels cell and thin film polarizers. 
    In addition, the study also demonstrated that a drifting direct current bias voltage of an electro-optic intensity modulator and a phase modulation could affect the SNR of the injection laser system. With a precise control of these factors, the injection laser system could output a nanosecond laser pulse with a SNR of 47.37 dB. 
    What is more, a nanosecond laser pulse SNR measuring device with a dynamic range and accuracy of 50 dB and 1 dB, respectively, was developed to detect the SNR of a nanosecond laser pulse, which was 47.06 dB within an accuracy range of 1 dB. The SNR measuring device can detect the high contrast laser pulse for the seed source unit in the high power laser facility precisely and conveniently. In this process, the SNR of an injection laser system should be orchestrated accurately to provide a high contrast laser pulse for the subsequent amplifier link in the high power laser facility. 
    The work, entitled "Detection and analysis of the signal-to-noise ratio in the injection laser system of the Shenguang-II facility", were published in Applied Optics Volume 57 Issue 34 2018.

Fig. 1 The phase modulation introduces an extra modulation.

Fig. 2 Effect of direct current bias voltage on the EOM and the SNR of laser pulse.

Fig. 3 The schematic diagram of a nanosecond laser pulse SNR detection device.

Fig. 4 The SNR of a 6 ns laser pulse in a seed source unit.

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Mr. Cao Yong
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS

@ Shanghai Institute of Optics and Fine Mechanics Tel:02169918000 Shanghai ICP NO.0501538