基于衍射理论的大非线性相移Z扫描研究

Study on Closed-aperture Z-scan Diffraction Theory for Large Optical Nonlinear Absorption Phase Shift

以衍射理论为基础,建立了强非线性吸收下,非线性介质对高斯光束的衍射模型.数值计算表明,折射相移的增大使峰的透过率增强而谷的透过率趋于饱和;而吸收相移的增大使峰的透过率被抑制而谷的透过率增强.相移比值是决定谷-峰结构存在与否的关键.在一定的输入功率下,远场输出功率并不是完全随着非线性吸收系数的增大而增大.该理论的近似条件只要求是薄样品,具有更好的适用性.

Based on Fresnel-Kirchhoff diffraction theory, a diffraction model of nonlinear optical media to gaussian beam was built for larger optical nonlinear absorption phase shift. Numerical results show that the peak of the transmittance is greatly enhanced and the valley is suppressed with larger refraction phase shift. While the large absorption phase shift＇ makes the peak of transmittance severely suppressed and the ,valley greatly enhanced. The ratio of these two phase shifts decide whether the valley-peak structure is existed. The far-field output power is not completely increased with the increasing nonlinear absorption coefficient. This theory is more accurately than the conventional Z-scan theroy because the applicable condition is only thin sample.