Coherent RayleighBrillouin Spectroscopy.
Abstract
Nonlinear optical spectroscopic techniques have been extended to the RayleighBrillouin region of the light scattering spectrum by studying the dispersion and polarization dependence of the optical Kerr effect, governed by (chi)('(3))((omega) = (omega) + (OMEGA)  (OMEGA)). As (VBAR)(omega)  (OMEGA)(VBAR) is tuned through zero in liquid CS(,2), two distinct resonant behaviors are observed. First, in a broad region extending a few wavenumbers about zero detuning there is a resonance due to opticalfieldinduced molecular reorientation. Analysis of the spectrum enabled the determination of the reorientation time of CS(,2), 2.0 psec. The polarization dependence of the reorientational signal agrees with theoretical predictions. We have thus demonstrated "Coherent Rayleighwing Spectroscopy". Second, by tuning the lasers to the acoustic phonon resonance at (VBAR)(OMEGA)  (omega)(VBAR) = .23 cm('1), we observe the Brillouin spectrum. This appears as an assymmetric doublet superimposed on the "Rayleighwing" background. The intensity dependence of the doublet is explained by a large signal treatment of the nonlinear optical process. We demonstrated, both theoretically and experimentally, the smooth transformation of the spectrum from the parametric limit, where the signal is proportional to (VBAR)(chi)('(3))(VBAR)('2), to a region where Stokes gain and antiStokes loss become evident. Thus we have demonstrated the dispersion and intensity dependence of "Coherent Brillouin Spectroscopy.". To overcome the experimental limitations of this study, we recommend Raman gain measurements be used for obtaining the absolute light scattering cross sections of material. In future investigations, it should be possible to measure the absolute Raman, electronic, Brillouin, and orientational contributions to the nonlinear susceptibility with high precision. A series of such measurements could then accurately quantify the light scattering parameters of standard samples. Finally, we study the dispersion of Brillouin induced phaseconjugate wave generation. In a smallsignal analysis, we predict the unique resonant properties of the "Brillouin Mirror" created by the enhancement of conjugate wave generation at the acoustic phonon resonances. By controlling the pump beam polarization, it is possible to control the apportionment of resonant reflectivity at two distinct Brillouin shifts. Thus the Brillouin nonlinearity may be used to construct a polarization tunable, phase conjugate resonant reflector.
 Publication:

Ph.D. Thesis
 Pub Date:
 1982
 Bibcode:
 1982PhDT........30J
 Keywords:

 Physics: Optics