High-fidelity fast-response phase conjugators for visible and ultraviolet applications

Abstract

The influence of bandwidth (2-800 GHz) and beam quality (2-70 X diffraction limit) on stimulated brillouin scattering (SBS), and consequently on phase conjugate reflectivity, threshold, and fidelity, have been investigated. Efficient stimulated scattering of broad-band poor beam quality radiation has been demonstrated. Broadband poor beam quality results show fair quantitative agreement with narrow-band good beam quality results, when scaling laws based on spot size, intensity, coherence length, and Rayleigh range are used. The influences of different SBS media and geometry are reported, predominantly at the XeCl laser wavelength of 308 nm, where phase conjugate cavities not requiring line narrowing are of great practical interest. The response time of the SBS process is investigated. Observations of response times much faster than the decay time of the acoustic wave in the medium are presented, demonstrating the potential of SBS for conjugating beams which display rapid (< 1 ns) spatial variations, such as those imposed on beams originating from discharge excited lasers. Experimental observations of the effect on SBS response of laser intensity are presented and interpreted with the aid of a semi-analytical expression which allows scaling to slower time- scales, longer pulses, and longer wavelengths.