Evaluation of third order nearly resonant optical nonlinearity of dye-doped films

由于染料掺杂聚合物薄膜易于制备，且在较低的连续激光功率下即可观察到非线性光学现象，因此在光学信息处理领域有着广泛的应用。本文采用几种测量方法对染料掺杂薄膜的三阶非线性系数进行了测量：（1）透射率与平面光束和高斯光束泵浦功率的关系（z扫描方法），（2）近简并二波混频的自衍射（移动光栅法）和（3）采用简并四阶相位共轭器的标准相位共轭干涉测量法测量泵浦透过率的方法简单，适用于三阶极化率虚部的计算。我们认为最合适的方法是移动光栅法，它适用于三阶极化率的真实的实部和虚部。期望更高的S/N测量来改善弱信号检测。相位共轭干涉测量法的实用性正在研究之中。对于吸收率较大的染料掺杂薄膜，z扫描法在评价光学非线性的简便性方面存在不足。

As dye-doped polymer films can be easily prepared and nonlinear optical phenomena are observed at relatively low powers of cw lasers, they are applied for optical information processings. It is desirable to develop the simple evaluation of the nearly resonant optical nonlinearity of dye-doped films.We evaluated the third order nonlinear susceptibility of the dye-doped films with several measuring methods of (1) the transmittance as a function of the pump powers of the plane beam and the Gaussian beam (z-scanning method), (2) self diffraction by nearly degenerate two-wave mixing (moving grating method) and (3) phase conjugate interferometry with a standard phase conjugator by degenerate four-wave mixing.The method of measuring the pump-transmittance is a simple one and applicable for the evaluation of the imaginary part of the third order susceptibility. We believe that the most suitable method is the moving grating one which is applied for real and imaginary parts of the third order susceptibility. The higher S/N measurement is expected to improve the weak signal detection. The usefulness of the phase conjugate interferometry is under study. For the dye-doped films with large absorbance, the z-scanning method is weak in the simplicity of the evaluation of the optical nonlinearity.