基于衍射模型的Z扫描理论

A New Z-Scan Theory Based on Diffraction Model

以菲涅耳基尔霍夫衍射理论为基础 ,建立了非线性光学介质对高斯光束的衍射模型 ,从一种新的角度解释了Z扫描现象。这种理论不仅在小非线性相移的情况下与传统Z扫描理论的结果完全一致 ,而且还适用于大非线性相移的情况。数值计算表明 ,随着非线性相移的增大 ,原来近似对称的Z扫描曲线发生畸变 ,谷的透过率被饱和抑制而峰的透过率被增强。

Based on Fresnel-Kirchhoff diffraction theory, a diffraction model of nonlinear optical media to Gaussian beam is set up, which can explain the Z-scan phenomenon from a new way. This theory is not only well consistent with the conventional Z-scan theory in the case of smaller nonlinear phase shift, but also can fit for the larger nonlinear phase shift. Numeric computations indicate the shape of the Z-scan curve is greatly affected by the value of the nonlinear phase shift. The symmetric dispersion-like Z-scan curve is only valid for small nonlinear phase shift (<π), but with increasing the nonlinear phase shift, the valley of the transmittance is severely suppressed and the peak is greatly enhanced. The laser power through the aperture will oscillate and attenuate as the nonlinear phase shift increases due to the increasing of the input laser power.