A comparative study of the coherent Raman processes using the ruby and the second harmonic neodymium giant-pulsed lasers

Results will be reported of stimulated Raman scattering using a giant pulsed green laser (5 289 Å radiation) on a large number of organic liquids. Ten megawatts of green radiation were produced by doubling 1,06 μ neodymium laser output in a KDP crystal through precision index matching techniques. Similar Raman scattering experiments using the radiation from a giant-pulsed ruby laser (6 943 Å) provided results for critical comparison studies of major differences of the two types of scattering observations. These will be discussed in detail. The key results include :1) Evidence that two-photon absorption is competitive with stimulated Raman scattering and is a quenching mechanism for the latter process when the laser frequency is approximately equal to one-half the frequency of an electronic absorption band of scattering sample. Moreover, some results on the inhibition of coherent Raman scattering are only explicable in terms of mixed two-photon (2νL — νR) + 2νL reactions, where νL and νR are the laser (1,06 μ) and Raman shifted frequency, respectively.2) Indications that the 5 289 Å laser is more efficient for producing SRS with some substances than is the ruby laser. A tentative explanation in terms of the wavelength dependence of self-trapping of laser beams is proposed.3) The stimulated Raman spectrum of benzonitrile contains shifts corresponding to two individual normal vibrations of the molecule and to sums and differences of these vibrations. Variations in the spectra obtained under different experimental conditions are discussed