Theoretical study on optical process in nanomaterial by using nonlinear susceptibility without cancellation terms

在光学非线性磁化率的序数表达式中，许多项相互抵消。如果我们留下抵消项，非线性磁化率在一个体极限内发散。为了避免这种非物理的结果，我们应该认真对待取消问题。到目前为止，石原和赵用一个简单的模型精确地处理了消去问题。然而，用非线性磁化率的序数表达式几乎不可能去掉第一性原理计算中的抵消项。在这个项目中，我们已经成功地推导了非线性磁化率的一般表达式，而不需要事先的抵消项。一般表达式帮助我们计算非线性磁化率的大小依赖关系，而不需要注意抵消项。我们还研究了微腔中激子的光学非线性响应。到目前为止，对空腔系统的光学非线性都是用半经典的方法研究的。然而，我们已经证明，为了研究腔系统的光学非线性，腔量子电动力学（cavity QED）是必不可少的。然后，我们研究了腔QED处理中的各种非线性过程。我们得到了在微腔中实现单量子点大光学非线性的最佳条件。我们研究了微腔中量子阱和量子点在超参量过程中产生的纠缠光子。由于空腔效应的存在，大大提高了发电效率。我们还找到了产生纠缠光子的最佳条件。从腔QED的特性特征可以定性地理解这些最佳条件。

In the ordinal expression of optical nonlinear susceptibility, many terms are cancelled with each other. If we leave the cancellation terms, the nonlinear susceptibility diverges in a bulk limit. In order to avoid this unphysical result, we should treat the cancellation problem carefully. So far, the cancellation problem was exactly treated in a simple model by Ishihara and Cho. However, it is almost impossible to remove the cancellation terms in the first principle calculation by usin the ordinal expression of the nonlinear susceptibility.In this project, we have succeeded to derive a general expression of nonlinear susceptibility without cancellation terms in advance. The general expression helps us to calculate size dependence of nonlinear susceptibility without attention to the cancellation terms.We have also studied optical nonlinear response of excitons in microcavity. So far, the optical nonlinearities of cavity systems were studied in a semiclassical treatment. However, we have shown that cavity quantum electrodynamics (cavity QED)is indispensable in order to study the optical nonlinearity of the cavity systems. Then, we study various nonlinear processes in the cavity QED treatment.1.We have derived optimal conditions for achieving large optical nonlinearity of a single quantum dot in microcavity.2.We have studied entangled photon generation due to the hyper-parametric process from a quantum well and quantum dot in microcavity. The efficiency of the generation is dramatically enhanced due to the cavity effect. We have also found optimal conditions for the entangled photon generation. These optimal conditions are qualitatively understood from the characteristic feature of the cavity QED.