Wave phenomena in nonlinear disordered optical media

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We investigated both experimentally and theoretically the wave phenomena in nonlinear disordered optical media.[1] Two-beam pump-probe method in space and time domainsWe proposed and theoretically analyzed a new method of two-beam pump-probe method in space and time domains. As a result, besides the signal term, which reflects the temporal and spatial response of material, we found parametric coupling phenomena that suggest that two laser beams injected onto the nonlinear disordered optical media are coupled through the fluctuation effect.[2] Stimulated emission and absorption in disordered mediumWe applied the above new technique to investigate the gain volume of random laser. In this experiment, two excitation laser beams just below the threshold of the random laser were injected on the disordered medium and the spectral width of the luminescence was monitor as a function of the spatial distance of two beams. We experimentally found that the gain volume is relevant to the transport mean free path and the absorption length and the volume is uniquely represented using an equation which includes these parameters. The computer simulation was also performed and the simulation well explains the experimental results.[3] Observation of the memory effect by using the parametric coupling phenomenaWe examined the memory effect, which means that waves in disordered medium still retain the information on the wavefront, using the above parametric coupling phenomena. We have clearly demonstrated the coupling phenomena by a series of detailed experiments on LiNbO3 as the nonlinear disordered medium.