JOINT STUDY ON OPTICS OF EXCITONS IN QUANTUM CONFINED SYSTEMS

目的是研究量子受限系统中激子的性质，并发展与激子有关的新的非线性光学现象。采用双光子吸收和单光子吸收相结合的方法测定了ZnSe/ZnS薄量子阱（QW）中的带偏。此外，由于约束效应，激子结合能（Ex）显著增强。然后，我们通过直接TPA首次在II-VI量子阱中发现了双激子的存在，并表现出新的发光线和PLE光谱。结果发现，20 *井厚下的双激子结合能（Exx）是体态znse的7倍。在ZnSe/ZnS量子阱中发现了两种新的非线性光学现象，即与2P激子共振的LO声子的“禁止”二次谐波产生（SHG）和超拉曼散射。基本方面通过实验得到了阐明，使我们能够解释微观机制。在晶格匹配的GaAs衬底上外延生长的ZnSe/ZnSxSel-x量子阱（x=0.18）中，实验研究了激子和双激子的性质。除PL和PLE外，还采用了新开发的新方法；分别是连续波布鲁斯特角（BR）反射光谱、飞秒瞬态BR反射光谱和BR几何结构中的四波混频（FWM）。首先，发现形成了单单层梯级结构，每个激子谱宽以均匀增宽为主。发现双激子稳定存在，在第二脉冲负延迟处存在FWM信号证明了这一点。与激子相比，Exx几乎是本体ZnSe的两倍。[00:05 . 4]在镶嵌在玻璃中的CdS和cur量子点中也发现了新的共振SHG和HR散射现象。

The purpose is to investigate the properties of exciton in quantum confined systems and to develop novel nonlinear-optical phenomena related to the excitons.1. The band-offsets in a thin ZnSe/ZnS quantum well (QW) were first determined with combined use of two-photon (TPA) and one-photon absorptions. Furthermore, a prominent enhancement of the exciton binding energy (Ex) due to confinement effect is found. Then, we have found the existence of biexciton for the first time in a II-VI QW by direct TPA,together with manifestation of a new luminescence (PL) line and the PLE spectrum. As a result, the biexcitonic binding energy (Exx) for 20 * well thickness is found to be 7 times as large as that of bulk ZnSe.2. Two novel nonlinear-optical phenomena, i.e., the "forbidden" second-harmonic generation (SHG) and hyper-Raman scattering by LO phonon both in two-photon resonance with 2P exciton are found in ZnSe/ZnS QWs. The fundamental aspects are experimentally clarified, enabling us to interpret the microscopic mechanisms.3. The properties of exciton and biexciton are experimentally studied in ZnSe/ZnSxSel-x QWs (x=0.18), epitaxially-grown on a GaAs substrate with latticematching. In addition to PL and PLE,novel methods newly-developed have been employed ; those are spectroscopies of cw Brewster-angle (BR) reflection, femtosecond transient BR reflection reflecting only free-induction decay and fourwave mixing (FWM) in the BR geometry. First, one-monolayr-terraced structure is found to be formed with each excitonic spectral width dominated by homogeneous brodening. A biexciton is found to stably exist, which is evidenced by the existence of the FWM signal in the negative delay of second pulse. It is found that Exx is almost twice enhanced as compared to that of bulk ZnSe, in contrast to that of exciton.13EA05 : 4. Novel resonant SHG and HR scattering phenomena are also found in CdS and CuBr quantum dots embedded in glasses.