Delay of the transient stimulated Brillouin scattering

Radiation emitted by a single-mode ruby laser (pulse duration 15 nsec) was used to stimulate the Brillouin scattering in liquid helium (4.2°K) and water and the Raman scattering in liquid nitrogen. At low values of the conversion coefficient, the maximum of the stimulated Brillouin scattering signal emitted from liquid helium and water was delayed relative to the maximum of the ruby pumping signal. The delay was 8–9 nsec in liquid helium and 2–3 nsec in water. No delay was observed tor the stimulated Raman scattering in liquid nitrogen. The delay increased with increasing relaxation time of the relevant excitations in the scattering medium.