Detection and analysis of the signal-to-noise ratio in the injection laser system of the Shenguang-II facility.

Abstract

The temporal contrast levels of laser pulses in the injection laser system of the Shenguang-II facility are accurately measured and analyzed in detail. These signal-to-noise ratio levels are determined by the extinction ratios of an acousto-optic modulator, an electro-optic intensity modulator, and a combination of a Pockels cell and thin film polarizers. In addition, a drifting direct current bias voltage of an electro-optic intensity modulator and phase modulation are also demonstrated to affect the signal-to-noise ratio of the injection laser system. With a precise control of these factors, the injection laser system can output a nanosecond laser pulse with a signal-to-noise ratio of 47.37dB. Moreover, a nanosecond laser pulse signal-to-noise ratio measuring device with a dynamic range and accuracy of 50 and 1dB, respectively, is developed to detect the signal-to-noise ratio of a nanosecond laser pulse, which is 47.06dB within an accuracy range of 1dB. The signal-to-noise ratio measuring device can detect the high contrast laser pulse for the seed source unit in the high power laser facility accurately and conveniently.