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，以获得对这项研究的相互理解。在银纳米晶体/玻璃复合材料中，我们研究了不同激励条件下飞秒区域的非线性响应：表面等离激元，带间（名古屋大学）和带内（Ecole理工大学）激励。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。在小于200fs的情况下，电子系统不显示费米分布，因为系统不处于平衡状态。此外，我们还观察到了由弹道声子散射引起的非线性响应的振荡行为。在稀释磁性半导体中，我们成功地利用激光烧蚀技术制备了直径为12 nm的CdMnTe纳米晶体。在CuCl纳米晶体中，由于激子和双激子态之间的量子干涉以及零声子和低声子辅助的受限激子跃迁之间的干涉，我们观察到了量子热现象。此外，我们首次观察到储存库的记忆效应，即。由于声子是受限的，所以受限激子的非马尔可夫相弛豫。最后，我们发现卤化铜纳米晶体中三阶磁化率的增强源于巨振强度效应，并且由于价带结构导致的双激子态和多激子态在大尺寸区域激子共振的非线性磁化率中起重要作用。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.