The Raman process has been extensively used with short wavelength excimer lasers almost since excimers were first made to lase in the mid 70's.(1,2,3) Operating in the ultraviolet, they are used to perform a variety of research and development tasks, as well as participate in a variety of commercial activities. They represent a major laser market and are available commercially around the world.
The application of Raman amplification to the problem of adaptive control over high-power lasers is reviewed. This particular application requires that no phase or intensity distortion present on the pumping laser be transferred to the phasefront of the Stokes beam. Several, recent experiments have shown that high-gain Raman amplification can preserve the phasefront of the output Stokes beam. These results are reviewed and compared to the predictions of theory.
Stimulated Brillouin scattering (SBS) allows control and transfer of phase among beams mixed in the SBS interaction volume. When beams are overlapped near the focal plane in an SBS cell, not only does wavefront reversal occur within each beam, but also the piston error between the beams is conjugated. Backseeding the SBS interaction volume with a low power beam results in SBS threshold reduction as well as a transfer of the phase of the seed beam to that of the Stokes return. This article provides a review of work performed which demonstrates and characterizes both techniques of SBS beam combination.
This review paper of the field of phase conjugation by stimulated Brillouin scattering (SBS) describes the fundamental work which has been performed to characterize the process, assess its ability to correct aberrations in an optical system, and evaluate its use in high energy laser applications. Basic characterization of the SBS process and scaling of threshold, reflectivity and conjugation fidelity are discussed. Work performed in the transient and CW regimes is reviewed. Experimental and theoretical investigations of multiline and broadband phase conjugation are presented.
The theoretical and experimental aspects of the use of stimulated Brillouin scattering (SBS) to compress laser pulses are reviewed. Several pulse compressor configurations are considered. The effects of laser linewidth and compressor geometry on conversion efficiency are discussed.
The technique of Brillouin induced four wave mixing (BIFWM) is currently receiving considerable attention because it can be used with pulsed lasers to achieve phase conjugation with extremely high reflectivities. Reflection coefficients in the region of 106 have been reported by some authors, and over 70% of the pump beam can be reflected into the conjugate beam, providing a very efficient usage of the pump beam energy . Using a variation of the technique it is alternatively possible to produce the phase conjugate of very weak signals corresponding to about 10-14J, or about 105 photons .
This paper presents a review of the various techniques for achieving vector phase conjugation and some results on a new method for laser beam combining based on multiwave optical mixing in atomic vapors.
This paper describes various beam coupling phenomena in photorefractive materials (e.g., BaTiO3, SBN, BSC)) ana their applications for wavefront control of laser beams. These beam coupling phenomena include two-wave mixing, four-wave mixing, self-pumped phase conjugation and mutually pumped phase conjugation.
Adaptive wavefront-correction concepts employing deformable mirror technologies have been under investigation for nearly four decades, but most of the important hardware advances have taken place in the last 15 years. State-of-the-art systems comprise second-generation components that are capable of simultaneously manipulating several hundred mirror actuators at kilohertz rates. In tests performed at visible wavelengths, these systems have demonstrated an ability to achieve near-unity Strehl ratios when coupled with telescopes having apertures in the 0.5 to 1-meter range. The third-generation technologies currently under development are intended to be scalable to transmitters of significantly greater dimensions.