A theoretical study is made of stimulated scattering of broadband radiation in a loop system with multiple intersection of the beams, operating at large (~π) scattering angles. It is shown that such a system could be used in phase conjugation of broadband pumping with an intensity much less than the critical value.
Various aspects of optical phase conjugation are discussed: the properties of the conjugate wave, its potential applications, the basic conjugation methods, and a brief history of the question. The theory for phase conjugation in stimulated scattering is set forth in detail. The basic experimental results on this conjugation method are also discussed in detail. Phase conjugation occurs because that configuration of the back-scattered field which has the conjugate wavefront is amplified to the greatest extent (at a doubled gain) in the intense speckle-inhomogeneous conjugate wave in a medium in which stimulated scattering occurs. Because of the large overall amplification in stimulated scattering, all the other, uncorrelated, configurations of the spontaneously scattered nucleating waves are amplified by a factor of 107 less and are discriminated against. The intervals of values of the various parameters in which the conjugate configuration (the specklon) exists are discussed theoretically, as is the effect of nonlinear selection and saturation on phase conjugation in stimulated scattering. There is a review of experimental results on the first observation of the effect, on the measurement of the angular structure of the uncorrelated waves and of the extent to which they are discriminated against, on the phase fluctuations of the conjugate wave, on the conjugation of subthreshold and depolarized radiation, and on phase conjugation in stimulated scattering in focused beams and for other scattered-wave amplification mechanisms.
We describe experiments investigating a technique that uses stimulated Brillouin scattering to phase conjugate a number of laser beams while preserving their relative phases. Phase locking of a number of beams focused into a stimulated Brillouin scattering cell is achieved by four-wave mixing with a pair of unfocused pump beams. The second pump is generated from the first by use of a stimulated Brillouin scattering loop geometry that minimizes phase fluctuations. We show that the reduction in phase fluctuations substantially improves the degree of phase locking. The requirements on four-wave mixing pump intensity are determined. The technique has the advantage of being insensitive to changes in alignment, with the potential to combine coherently a large number of laser amplifiers in a simple and compact geometry.
As it is known, self-conjugation of the IR laser beam via Brillouin radiation stimulated scattering phenomenon is not realised because of some physical limits on radiation intensity which are the principal limitations, to the present time. That is why, one of the promising technique of phase conjugation of infrared radiation is a self-conjugation of a laser beam wavefront via four wave interaction in a nonlinear medium with feed-back loop (FWMF) [1]. Unlike conventional our wave mixing schemes, the FWMF self-conjugation is supposed to be realised without any additional beams pumping a phase conjugation mirror.
A system for phase conjugation of Stokes radiation by a four-wave interaction involving intracavity stimulated Raman scattering (STRS) in a Raman-active medium with a nonresonant nonlinearity. This method can be used in construction of high-power sources of highly directional Stokes radiation on the basis of round-trip STRS amplifiers coupled to a phase-conjugating element. It is shown that an STRS converter utilizing organic liquids and subjected to laser pumping of less than 100 MW/cm2 intensity inside a resonator can ensure a highly efficient phase conjugation with a peak reflection coefficient in excess of unity. Depending on the ratio of the Raman and nonresonant susceptibilities of a medium, there is an optimal value of the coefficient representing the degree of conversion of laser pump radiation into STRS radiation, which ensures the maximum phase conjugation efficiency.