Stimulated Raman scattering of titanium-sapphire laser pulses with duration from 7 ps to 45 ps in BaWO$_4$ crysral

Transient stimulated Raman scattering of titanium-sapphire laser pulses with varying duration in a BaWO$_4$ crystal was experimentally studied at its dominant mode $\nu_1$ = 925 cm$^{-1}$ with the dephasing time $T_2\sim$6.6 ps. For pulses with a duration of 7–17 ps (corresponding to $\sim T_2$ – 2.5$T_2$), the maximum conversion efficiency was $\sim$1%, which was achieved at the same laser pulse fluence of 1.2 $\pm$ 0.2 J/cm$^2$. At a pulse duration of 45 ps ($\sim$7$T_2$), the SRS conversion efficiency was 7 times higher ($\sim$7%), and the SRS “threshold” fluence was 2 times lower. It has been shown that to reduce the threshold and to increase the efficiency of stimulated Raman scattering, the femtosecond pulse should be stretched in time at least to $\sim$7$T_2$.