Effects of Stimulated Raman Scattering on Light Beam Properties During High-Power Laser Beam Long-Path Propagation
FOREIGN AEROSPACE SCIENCE AND TECHNOLOGY CENTER WRIGHT-PATTERSON AFB OH
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Beginning from the third-order nonlinear polarization from the stimulation and induction of matter based on the semiclassical theory of stimulated Raman scattering SRS, a theoretical model of coupling between the phase of a pump transmission laser beam and the phase of the Stokes beam intensity is established for the case of stimulated Raman scattering during long-path propagation of a high-power laser. The model clearly explains how the SRS effect influences the beam properties of the pump laser, including the physical regime and effective factors of time-domain properties and space-domain properties light beam quality. The theoretical analysis is in fairly satisfactory agreement with the experimental results. In the experiments, measurements of time-domain properties were taken of the pump laser beam and the Stokes beam after transmission in a situation with various conversion efficiencies Ns. As shown by the results, under conditions of low-conversion efficiencies, basically the time-domain properties of the pump laser beam are not affected by the SRS effect. But when the conversion efficiency Ns is greater than 5 percent, the pulse duration of the pump laser beam is gradually reduced as Ns is increased. Stimulated raman scattering, Pump laser beam, Stokes beam, Far-field divergency angle.
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