Formation and amplification of uitrashort optical pulses as a result of stimulated scattering in opposite directions

It is shown that the growth and contraction of a Stokes pulse formed as a result of stimulated Brillouin scattering are not limited by the hypersound relaxation time T_r (or, in the case of stimulated Raman scattering in opposite directions, by the transverse relaxation time T₂). Amplification of a pulse of duration T_s < T_r is analogous to the propagation of a transient π pulse in a two-level laser amplifier. In a long stimulated-scattering amplifier a Stokes pulse always assumes a quasiself-similar profile which retains memory only of the leading edge of the input pulse; during propagation this pulse collects all the pump radiation energy and contracts so that its area remains constant and approximately equal to π/2. A study is made of the conditions under which such pulses form from spontaneous noise and it is demonstrated that a high degree of reduction of the pump pulse duration is possible in the course of stimulated Brillouin scattering in rare gases and this may be accompanied by an increase in the power by a factor of the order of 10².