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，且在较低功率的连续波激光下可观察到非线性光学现象，因此可用于光学信息处理。建立染料掺杂薄膜近共振光学非线性的简单评价方法是很有必要的。我们采用了几种测量方法来评估染料掺杂薄膜的三阶非线性磁化率：(1)透射率作为平面束和高斯光束泵浦光强的函数（z扫描法），(2)近简并双波混频自衍射（移动光栅法）和(3)简并四波混频相位共轭干涉法。测量泵浦透过率的方法简单，适用于三阶磁化率虚部的计算。我们认为最合适的方法是移动光栅法，它适用于三阶磁化率的实部和虚部。高信噪比的测量有望改善微弱信号的检测。相位共轭干涉术的有效性正在研究中。对于大吸光度的染料掺杂薄膜，z扫描方法在评价光学非线性的简捷性方面较弱。

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.