Stimulated rotational Raman scattering in air with a high-power broadband laser

We study the growth of stimulated rotational Raman scattering (SRRS) from noise by propagating one beam of the OMEGA fusion laser over a 35-m path in air. The spectrum at the end of the path is measured and calibrated to give the energy scattered into all the Stokes lines. Pure phase-modulated bandwidth as well as the bandwidth known as smoothing by spectral dispersion (SSD) are installed on the laser. The experimental results show that the threshold for SRRS is unchanged when one uses a pure phase-modulated bandwidth and increases when one uses a SSD bandwidth.