Joint Study on nonlinear optics in nanostructured materials

我们研究了纳米结构材料的非线性光学性质，为光子器件材料的发展提供了指导原则。我们交换了法国和日本团队的研究人员，进行了实验和讨论，以获得对本研究的相互理解。在银/玻璃复合材料中，我们研究了飞秒时间区域内不同激发条件下的非线性响应：表面等离子体激元，带间（名古屋大学）和带内（巴黎综合理工学院）激发。我们发现响应时间为几ps的非线性响应是由热电子效应引起的，非线性折射率为负。对于小于200 fs，电子系统不显示费米分布，因为系统不处于平衡状态。此外，我们还观察到了由于弹道声子散射引起的非线性响应的振荡行为。在稀磁半导体中，我们利用激光烧蚀技术成功地制备了直径为12 nm的CdMnTe纳米晶。在CuCl纳米晶体中，我们观察到了由于激子和双激子态之间的量子干涉以及受限激子的零声子和LO声子辅助跃迁之间的干涉而引起的量子拍频现象。此外，我们还首次观察到了储层的记忆效应，即储层的非线性效应。由于声学声子被限制，限制激子的非马尔可夫相位弛豫。最后，我们发现卤化铜纳米晶的三阶非线性系数的增强是由巨振子强度效应引起的，并且由于价带结构而产生的双激子态和多激子态对大尺寸区域激子共振下的非线性系数起着重要的作用。这些结果为我们在纳米尺度上开发非线性光学材料提供了指导原则。

We have studied nonlinear optical properties of nanostructured materials to investigate a guiding principle for development of photonic device materials. Exchanging the researchers in French and Japanese teams, we performed experiments and discussed to get mutual understanding of this study. In silver nanocrystal/glass composites, we investigated the nonlinear response in a femtosecond time region with different excitation conditions : surface plasmon, interband (Nagoya University) and intraband (Ecole polytechnique) excitations. we have found that the nonlinear response with a reponse time of a few ps is originated from hot electron effects and nonlinear refractive index is negative. For less than 200 fs, the electron system does not show the Fermi distribution because the system is not in equilibrium. Furthermore, we have observed oscillation behaviors in nonlinear response due to ballistic phonon scattering. In diluted magnetic semiconductors, we have succeeded to fabricate CdMnTe nanocrystals with a diameter of 12 nm by means of the laser ablation technique. In CuCl nanocrystals we have observed quantum beat phenomena due to the quantum interference between exciton and biexciton states and the interference between the zero-phonon and LO phonon assisted transition of confined excitons. Furthermore, we have observed, for the first time, the memory effect of the reservoir, ie. the non-Markovian phase relaxation of confined excitons since acoustic phonons are confined. Finally, we have found the the enhancement of third-order susceptibilities in copper halide nanocrystals is originated from the giant oscillator strength effect, and the two-exciton state and the multiexciton states due to the valence band structure play an important role in nonlinear susceptibilities at the exciton resonance in the large size region. These results give us a guiding principle to develop nonlinear optical materials on the nanometer scale.