TRANSIENT TRANSVERSE STIMULATED BRILLOUIN-SCATTERING WITH A BROAD-BAND PUMP

Transverse stimulated Brillouin scattering (SBS) can damage optical components and be an energy loss mechanism in high-power pulsed laser systems. The threshold for SBS can be increased by using a broad-band laser or by segmenting the aperture in order to limit the interaction length. In this paper we develop a theoretical model of transient broad-band SBS. We start by considering the case of transient SBS with a monochromatic pump and find the effective interaction length for a pump pulse of a given duration. Using this interaction length, we derive expressions for the threshold intensity and for the window size required to avoid SBS with a pulse of given power and duration. Next we compute the steady state gain and threshold intensity as a function of bandwidth for a multimode laser with large mode spacing. We find that the ratio of the broad-band threshold intensity to the threshold intensity for a monochromatic pump is determined by the ratio of the bandwidth to the actual gain per unit length at threshold. Numerical simulations indicate that the same dependence applies to transient SBS.