ZnS/CdSe量子点中线性和三阶非线性光吸收系数研究

Linear and Nonlinear Optical Absorptions in a ZnS/CdSe Quantum Dot Quantum Well

在有效质量近似下,利用量子力学的密度矩阵理论,采用无限深势阱模型,从理论上研究了ZnS/CdSe柱型核壳结构量子点中线性和三阶非线性光吸收系数。导出了柱型量子点中线性和三阶非线性光学吸收系数的解析表达式,分析了该系统在不同条件下线性和三阶非线性光吸收系数与入射光频率之间的关系。改变系统的参数,该系统的光吸收系数呈规律性变化。计算结果表明:弛豫时间τ、入射光强I和壳半径R2对系统的吸收系数α有很大的影响,从而为实验上研究核壳结构量子点的非线性光学效应提供了必要的理论依据。

In the effective mass approximation,we calculate the energy and wave function of a core-shell quantum dot.The linear and the third-order nonlinear optical absorptions in the core-shell quantum dot are investigated theoretically.The analytical expressions of the linear and the nonlinear optical absorption coefficients are obtained by using the compact density-matrix formalism and the iterative proceduce.The numerical calculations are presented for a ZnS / CdSe core-shell quantum dot.The results show that the factors of the incident optical intensity I,the relaxation timeτand the quantum dot size of the system have a great influence on the optical absorption.The total optical absorption coefficients enhanced are obvious with the relaxation time increasing.Moreover,the line width will broaden as the relaxation time decreases.This peak will significantly enhance with the incident optical intensity increasing,which directly affects the total optical absorption coefficients.The optical absorption saturation will occur when the incident optical intensity is I=1.0×10 10 W/m 2.When the optical intensity exceeds this value(I=1.5×10 10 W/m 2),the total absorption peak can be split up into two peaks.