强非线性吸收下Z扫描衍射模型及实验研究

根据光的衍射理论,建立了非线性光学介质对高斯光束的开孔Z 扫描理论模型.数值计算表明,当相移比值Γ≤0.15,出射光功率随入射光功率的增加出现振荡衰减现象;当Γ>0.15,在输入光强低于某一个值时,输出随输入的增加而线性增加;当输入光强超过该值后,输出功率不再增加甚至趋于零.实验采用Nd∶YAG脉冲激光,在波长为532 nm,脉宽8 ns条件下,对含3.5%和7.0%碳纳米管的聚苯胺/碳纳米管复合体薄膜（PANI/MWCNT）的非线性吸收特性进行了研究.计算表明,该类化合物的激发态吸收截面积远大于其基态吸收截面积,具有很强的反饱和吸收.

Diffraction Z-scan Theory and Experiment with Strong Nonlinear Absorption

Based on Fresnel Kirchhoff diffraction theory,the propagation behavior of the gauss beam passing through the nonlinear optical medium without aperture was theoretically deduced and numerically simulated.Numerical results show that the output power is attenuated and surged with the increased input laser power when pahse shift ratio Γ is equal or samller than 0.15,and the optical limiting phenomenon is observed when Γ is larger than 0.15.The nonlinear absorption properties of polyaniline/carbon natotube composite films were investigated using 8 ns pulses at 532 nm.The experimental results show that the compound owns strong reverse saturable absorption which excited state absorption cross section is larger than the groud state absorption cross section.