应用Top-hat Z-scan技术在波长为532 nm, 脉宽为190 fs激光脉冲下研究了CdTe和CdS量子点的光学非线性吸收和非线性折射特性。实验结果表明: 在飞秒激光脉冲作用下, CdTe量子点的非线性吸收表现为饱和吸收, CdS量子点表现为反饱和吸收。CdTe量子点的非线性折射表现为自散焦, CdS量子点表现为自聚焦。尺寸分别为2.6、2.4 nm 的CdTe量子点和CdS量子点的非线性吸收系数分别为-9.26×10-14、0.78×10-14 m/W, 非线性折射率系数分别为-0.86×10-20、1.46×10-20 m2/W, 三阶非线性极化率分别为2.72×10-15、1.36×10-15 esu。表明相近尺寸下不同材料的镉类半导体量子点的光学非线性吸收和非线性折射特性不同, 并对其机理进行分析。

The optical nonlinear absorption and nonlinear refraction properties of CdTe and CdS quantum dots(QDs) were investigated by Top-hat Z-scan technique. The experimental condition of Top-hat Z-scan was at a wavelength of 532 nm and a pulse width of 190 fs. Under the the action of femtosecond laser pulses, the experimental results show that the nonlinear absorption of CdTe QDs is saturable absorption and the nonlinear absorption of CdS QDs behave as reverse saturable absorption. The nonlinear refraction of CdTe QDs self-defocusing, and CdS QDs show self-focusing. The nonlinear absorption coefficients of CdTe QDs and CdS QDs with dimensions of 2.6 nm and 2.4 nm are -9.26×10-14 m/W, 0.78×10-14 m/W, respectively, and the nonlinear refractive index coefficients are -0.86×10-20 m2/W, 1.46×10-20 m2/W, respectively, and the third-order nonlinear polarizabilities are 2.72×10-15 esu and 1.36×10-15 esu, respectively. It was shown that the optical nonlinear absorption and nonlinear refraction of cadmium semiconductor QDs with different materials under the similar sizes are different. Based on the experimental results, the mechanism was analyzed.