Nonlinear Sagnac interferometry for improving signal-to-noise ratio of short pulse

This paper demonstrates several factors that affect the signal-to-noise ratio(SNR) improvement ability and the energy conversion efficiency of nonlinear Sagnac interferometry. The efficiency can be improved by controlling the spatial distribution of pulse and the transmittance of attenuator. The SNR improvement ability is related to the SNR of input pulse: higher input pulse SNR enhances the SNR improvement. The experimental platform was established on SILEX-Ⅰ laser facility. The ultra-short pulse from 3 TW compressor was attenuated and sent into the Sagnac loop. The nonlinear medium was a 5 cm long fused silica material and the attenuator transmittance was 55%. When the input pulse energy is 6.6 mJ, the pulse SNR is improved from 10-6 to 10-7 by third-order autocorrelator. The energy of the output pulse is 1.6 mJ, with efficiency about 24%. This method has no limit to the beam diameter, and thus can be used for short-pulse SNR enhancement in the large energy conditions.