非线性相移对Z-scan曲线对称性的影响
Effect of nonlinear phase shift on symmetry of Z-scan curves
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摘要: 基于由光束传输的ABCD矩阵得出的Z-scan透过率的解析结果，分析了Z-scan实验曲线随非线性相移的变化规律。发现随着相移的增加，折射非线性相移比吸收非线性相移对Z-scan曲线对称性的影响更大。对于具有强饱和吸收和弱自聚焦特性的非线性介质，其Z-scan曲线随非线性折射相移的变小将失去典型的类色散特点。对于1μm厚的ZnCdSe-ZnSe多量子阱，扫描光源采用532 nm的基模高斯光束，采用透过率表达式来拟合所得的实验数据，在吸收非线性相移为0.9与耦合因子为-10条件下，推算出三阶非线性吸收系数为2×10-3 cm/W，三阶非线性折射系数为 8.0×10-8 cm2/W，这与J.Ma等人的结果吻合。最后对曲线特征参数随非线性相移变化进行了数值计算，得到的曲线所对应的非线性相移与曲线谷位置的乘积近似为一常量，值为0.166。Abstract: Based on the simulated results of normalized Z-scan transmittance by using ABCD formalism and q parameter, analysis on the variational characteristics of Z-scan curves with nonlinear phase shifts proves that the asymmetry of the curve is more greatly affected by nonlinear refractive phase distortion than by nonlinear absorptive one, and that the Z-scan curves of a certain media with strong saturated absorption and weak self-focusing third-order nonlinearity will not hold the dispersive-like characteristics any more. With the absorptive nonlinear phase shift of 0.9 and coupling factor of -10 in the transmittance expression, the fitting with the experimental data for ZnCdSe-ZnSe(MQWs) of 1 μm thickness conducted with 532 nm TEM00 brought in almost the same results of third-order nonlinear
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Key words:
- nonlinear phase shift /
- z-scan method /
- quantitative analysis /
- dispersive-like /
- asymmetry
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