Amplified spontaneous emission enhanced forward stimulated Raman scattering in dye solutions

We study forward stimulated Raman emission from the weakly fluorescent dye 4^′-diethylamino-N-methyl-4-stilbazolium tosylate (DEST) in 1,2 dichloroethane solution excited by a 28-ps, 532-nm Nd:YAG laser. Neat 1,2 dichloroethane emits the first Stokes line at 631 nm with a spectral width of 1.6 nm, corresponding to a Raman shift of 2956 cm^-1. We observe a reduction of spectral width with the addition of DEST in 1,2 dichloroethane solution. The single-pass conversion efficiency for forward Raman emission is as high as 10% in a 1-cm-path-length sample. The pulse duration of forward stimulated Raman emission, measured by a third-order autocorrelation technique, is 10 ps in neat 1,2 dichloroethane, whereas it is ～3 ps for 4×10^-5 mol/l of DEST solution.