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，以探索发展光子器件材料的指导原则。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，以加深对本研究的理解。在银纳米晶/玻璃复合材料中，我们研究了不同激发条件下飞秒时间段的非线性响应：表面等离子体激发、带间激发(名古屋大学)和带内激发(Ecole Polytech)。我们发现响应时间为几个ps的非线性响应是由热电子效应引起的，并且非线性折射率为负。在小于200fs的范围内，由于电子系统处于非平衡状态，电子系统不呈现费米分布。此外，我们还观察到了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出了直径为12 nm的纳米晶。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限制激子的零声子和LO声子辅助跃迁而产生的量子拍频现象。此外，我们还首次观察到了水库的记忆效应，即记忆效应。声学声子禁闭后受限激子的非马尔可夫相位驰豫。最后，我们发现卤化铜纳米晶中三阶极化率的增强源于巨谐振子强度效应，而由价带结构引起的双激子态和多激子态在大尺寸激子共振时的非线性极化率中起着重要作用。这些结果为在纳米尺度上发展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.