基于衍射理论的Z扫描技术分析与数值模拟

Technical analysis and numerical simulation of Z-scan characteristics using Fresnel-Kirchhoff diffraction theory

以菲涅耳-基尔霍夫衍射理论为基础,对通过非线性介质的高斯光束传输行为进行理论分析,分别给出了强吸收、无吸收情况下开孔、闭孔Z扫描曲线公式;对不同条件下非线性介质的归一化透过率进行数值模拟计算,发现Z扫描曲线透射峰和透射谷表现出3种新的特性:随着入射激光峰值光强的增加,Z扫描曲线透射峰的高度受到抑制,而透射谷则加强变得更深;非线性相移的增加对Z扫描曲线透射峰和透射谷均有增高和加深的作用;激光束束腰半径越大,Z扫描曲线的峰谷特征越明显。

Based on Fresnel-Kirchhoff diffraction theory, the propagation behavior of the Gaussian beam passing through the nonlinear optical medium is theoretically analyzed under strong absorption or without absorption. A unified equation is derived, which can describe the open-aperture Z-scan curve and the closed-aperture Z-scan curve. The numerical simulation of Z-scan curve under different conditions shows that the transmission Z-scan curve with peak and valley has some new features. As the incident laser peak intensity increases, the transmittance peak is suppressed and the valley is strengthened; increasing of nonlinear phase shift can heighten the peak and deepen the valley; the larger the laser beam waist radiusis, the more obvious the features of peak-valley configuration are.