An analysis of high efficiency stimulated Raman scattering in water with a frequency-doubled pulsed Nd:YAG source

Abstract

Abstract Unexpectedly high stimulated Raman scattering (SRS) has been seen with a frequency-doubled Nd:YAG pump laser (532 nm) in water. The pump beam was propagated, both focused and unfocused, through a 4m long tank. Threshold pump irradiance for SRS was measured to be 2 × 1013 Wm−2 and Stokes transitions were identified at approximately 3230 and 3380 cm−1. The maximum conversion efficiency to the Stokes frequencies seen was 13% of pump input, for a focused beam, 4% for unfocused. SRS from an unfocused beam was seen to arise from high irradiance filaments caused by self-focusing in the water. The term Raman Interaction Function (RIF) has been defined here as the irradiance of the pump beam integrated over the interaction length (distance over which the pump beam irradiance is above threshold). The RIF model was been designed to describe the relationship between pump laser parameters and the output at the dominant Stokes frequencies.