Abstract

Efficient conversion in Raman beam combination systems with preservation of the Stokes seed phase front and temporal coherence is dependent on pumping geometry, mode spectrum, and relative intensities of lines in multiwavelength operation. Beam cleanup with highly aberrated narrow-line single-wavelength pump beams is shown to be a function of injection angle, Fresnel number, and gain saturation. In multimode operation, however, the loss of correlation between pump and Stokes beams during amplification as well as the influence of injection angle in establishing and maintaining a phase-locking condition will affect efficiency. Nonlinear dispersion, four-wave mixing of pump/Stokes modes, and mixing of lines at phase-matching angles in multiline conversion will be factors affecting the beam quality of the output Stokes and the generation of higher orders. Analytical and numerical results for conversion of single-line and two-line XeF in H₂ are given for both narrowband and broadband operation. Results are presented on the use of phase conjugation to correct for component and distributed medium aberrations in a Raman amplifier used in beam combining applications as a function of pump beam aberration, degree of Raman medium aberration, phase conjugator reflectivity, injection angle, and Fresnel number.

© 1985 Optical Society of America