Abstract

Stimulated rotational Raman scattering in hydrogen has been shown to be an extremely efficient mechanism for frequency con version and optical beam combining.¹ In this work we have investigated deuterium as a rotational Raman medium. A frequency-doubled Q-switched Nd:YAG laser was used to pump a single pass 0.5-m Raman cell containing deuterium gas at densities between 1 and 10 amagats. Conversion into rotational and vibrational Stokes and anti-Stokes orders was measured as a function of deuterium pressure, laser power, and focusing geometry. By using circularly polarized pump light, it was possible to suppress all Raman orders except first rotational Stokes and to obtain an overall energy conversion efficiency of 72% into first Stokes at pressures between 4 and 6 amagats. Time-resolved oscillograms of the pump and Raman laser outputs show that during the first 2 ns of the 8-ns FWHM pump pulse Raman conversion is suppressed, while during the remainder of the pulse conversion to the first rotational Stokes proceeds with near unit quantum efficiency. The initial delay in onset of the Raman process is thought to arise from the transient buildup time associated with the relaxation time of the Raman medium.

© 1986 Optical Society of America