Phase-locking and self-phase matching in nonlinear optics

Thesis (Ph. D.)--University of Rochester. Institute of Optics, 1998.Laser and optical systems contain components that can aberrate the optical wavefront and the polarization of a beam of light. These aberrations can originate from material distortions, thermal distortions, stress induced birefringence, or other physical factors. Often it is not feasible to correct for these aberrations using linear optical components. Nonlinear optical vector phase conjugation is one method that can completely correct for distortions of this sort. Certain geometries of Brillouin-enhanced four-wave-mixing (BEFWM) can achieve near perfect vector phase conjugation. Three different geometries were studied. It was found that the geometries with focused probe beams had superior vector phase conjugation properties. Experimental results show that this vector phase conjugation process can compensate for a depolarization as large as 50% to produce a beam in which the residual depolarization is less than 4%. The BEFWM geometries studied in this dissertation have the property that the phase ofthe probe conjugate is set by the phases ofthe pump and probe beams. This phase locking of the probe conjugate allows phase coherent combining of multiple beams that have been conjugated in parallel. By judicious choice of the phases of the probe beams prior to recombination, the combined beam may exactly retrace its path, or select a different path to couple energy out of the system. Beam combining and output coupling efficiencies of >99% were experimentally observed simultaneously with vector phase conjugation. "Diffractionless" beams, such as Bessel beams, have been known for some time and can be used to enhance certain nonlinear optical interactions. A complete theory for self-phase-matching in third harmonic conversion using "diffractionless" beams is presented in this dissertation. A generalization of the Bessel beam, which I call the asymmetric "nondiffracting" beam, is described in detail. This asymmetric class of beams display advantages over ordinary Bessel beams for certain nonlinear optical processes. Experimental results are presented which show that the small central spot of an asymmetric beam can contain >80% of the beam energy and persist for more than 5 meters of propagation