Study on the Phase Dynamics of Macroscopic Polarization by Nonlinear Interferomer

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In order to explore the mechanism of ultrafast coherent third order nonlinear responses in solid materials, we have developed a method to detect the coherent motion of macroscopic polarization created by the optical excitation. By this method, we can investigate phase coherence of resonantly excited excitons and biexcitons in inorganic and organic materials.1)Nonlinear InterferometerWe have proposed a scheme to measure the coherence of third-order nonlinear polarization by detecting the interference of degenerate four-wave mixing signal and reference optical pulses which were also from the same light source used to create coherent excitation of nonlinear polarization. With this set-up, we have detected the coherent oscillation of nonlinear polarization.2)Observation of Coherent Oscillation of Biexcitons in CuClThe coherent oscillation of biexcitons under the resonant two-photon excitation by femtosecond pulses has shown that the coherent oscillation continues up to 50 picosecond.3)Inte … More rference of Scalar Biexciton WavesWe have observed the interference of two biexciton waves which were excited by the orthogonally polarized pump beams. This indicates that the biexciton wave has the scalar wave nature. This is, to the best of our knowledge, the first time observation of scalar wave interference in solids.4)Detection of two-exciton coherence in GaAs quantum wellWe have applied the above methods to the 2D quantum well excitons which do not have stable biexciton state. We have clearly observed 2-f coherent oscillation which decays within 3 picosecond.5)Free Induction Decay of 2D Excitons in Anthracence crystalsBy using the coherent pump-probe spectroscopy, we have observed coherent oscillation signal of surface excitons in an anthracence crystal. We have examined the role of cooperative radiation decay of surface excitons, which is known as superradiative decay of 2D excitons.6)Degenerate Four Wave Mixing of Exciton-Cavity Coupled SystemWe have studied the linear exciton-photon coupling effect on the coherent nonlinear optical responses of excitons in 2D quantum well embedded in a semiconductor microcavity. We have observed that the strong confinement of photons inside the cavity enhances the coherent noonlinear responses. In the case of strong exciton-photon coupling, the formation of cavity polartons affects the coherent oscillation of excitonic polarization. We have developed a theoretical model to describe such phenomena based on the weakly interacting boson model. Less