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Proceedings Paper

Effect On Beam Quality Of Lransient Refractive-Index Changes In Stimulated Raman Scattering
Author(s): A. Flusberg; D. Korff
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Paper Abstract

Two sources of phase aberrations during amplification by stimulated Raman scattering have been studied. Both are caused by intensity nonuniformity in the incident pump laser beam. First, nonuniform population transfer of molecules undergoing the Raman transition results in a cumulative refractivity nonuniformity associated with the difference between the polarizabilities of the two molecular states. As shown experimentally by Butylkin et al. and Baklushina et al., the fractional polarizability difference for the Q(l) vibrational transition of H2 is ≈0.15-0.20. As a result, this effect becomes large at a fluence nonuniformity level >33/cm2. The dependence on fluence, rather than intensity, arises from the cumulative population transfer that takes place when the relaxation of the upper level during the laser pulse only weakly affects the population difference. Second, collisional relaxation of the excited population during the pulse causes heating and a nonuniform density distribution; this effect becomes more important as the pulselength is increased or the spatial scale size of the intensity gradients is decreased. The equations coupling the pump and Stokes fields to the refractivity and density changes are solved in the ray-optics limit of collimated beams and the effect on beam quality is determined. It is shown that in the limit of weak refractivity effects and negligible heating the beam-quality loss varies as the square of the rms fluence modulation.

Paper Details

Date Published: 25 November 1986
PDF: 8 pages
Proc. SPIE 0642, Modeling and Simulation of Optoelectronic Systems, (25 November 1986); doi: 10.1117/12.975491
Show Author Affiliations
A. Flusberg, Avco Everett Research Laboratory, Inc. (United States)
D. Korff, Avco Everett Research Laboratory, Inc. (United States)

Published in SPIE Proceedings Vol. 0642:
Modeling and Simulation of Optoelectronic Systems
John Dugan O'Keefe, Editor(s)

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