Polarization-resolved beam combination in liquid suspensions of shaped microparticles

Abstract

We have observed and developed a theory for polarization-resolved two-beam coupling via nondegenerate two-wave mixing in water-glycerol suspensions of shaped polytetraflouroroethylene microparticles. Experiments detected energy transfer driven by two different classes of moving optical index gratings: density and orientational. These gratings arise from and reflect translation of the microparticle's center of mass and rotation of its symmetry axis by laser-induced electrostrictive forces and torques. Each grating features its own response time, frequency response, and polarization characteristics. The steady-state and transient dynamics of moving shaped microparticle optical index gratings were studied by measuring the energy diffracted by these two gratings from one beam to the other. The dependence of the two-wave-mixing gain coefficient on beam polarization, laser frequency difference, pump intensity, and volume fraction was measured and found to be in accord with theory. Furthermore, the evolution to steady state was examined, with theory and experiment in good agreement. Finally, beam combination was also achieved using degenerate laser beams and moving the suspension relative to the laser interference pattern. © 1991 The American Physical Society

Measurements of light-scattering noise accompanying two-wave mixing in a Kerr medium

“…2(b). Note that both the experimental and theoretical gain profiles follow frequency dispersion curves characteristic of the Debye relaxation model [8,10]. More importantly, there is excellent agreement between theory and experiment in regard to the rms values of the noise fluctuations, including their dependence on frequency shift.…”

“…The beam waist size is about 100 pm and the interaction length is 0.1 cm. Before entering the sample, the polarization direction of the pump beam is rotated perpendicular to that of the probe so that only the orientational-particle gratings are generated in the suspension by the beam interference pattern [10].…”

“…Implementing this setup, particular care had to be taken to damp mechanical vibrations that could add random phase shifts to the beams, thus introducing spurious noise in the gain process. wherẽ =~& =8,9 ms is the orientational response time as determined through independent measurements [10]. Each vertical bar is centered on the average value of the transmitted power and the bar length reports the rootmean-square (rms) value of the noise fluctuations on the same scale.…”