Abstract

Raman beam clean-up and aperture combining, currently a topic of intense research, improves the spatial mode of coherent light sources by using stimulated Raman scattering to amplify a high quality Stokes beam. Energy is transferred from several high intensity pump beams to the Stokes seed beam by crossing the pump beams at small angles to the Stokes beam. Thus the angular dependence of the Raman gain needs to be characterized before this beam clean-up process can be accurately modeled. For pump and Stokes beams that are collinearly polarized, the angular dependence of the gain originates from the angular dependence of the linewidth. We have measured the linewidth of the Q(1) H₂ Raman line for angles of 0-165° and densities of 1-25 amagats by fitting the profiles to Lorentzians, which provide good fits for these data. These measured linewidths are compared to empirical models; the most accurate model predicts linewidths to within 5% of our measurements for all angles and densities. We plan to make measurements with improved signal/noise to fit to Galatry profiles¹ to directly extract the collisional narrowing contribution.

© 1986 Optical Society of America