Generation of Phase-Conjugate Waves in Saturable Dye-Doped Films and Transient Properties of Phase-Conjugated Waves

染料掺杂透明聚合物薄膜的光学相位共轭已引起人们的关注。某些杂蒽染料和偶氮染料在氩离子激光波长处有很强的吸收，其激发态的寿命也相对较长，这使得在低于0.5w/cm^2的低强度下产生连续波相位共轭波成为可能。采用浸渍法和旋涂法分别制备了厚（10-100 m）和薄（<10 m）的染料掺杂聚合物薄膜。产生相位共轭波的主要机理是：(1)染料可饱和吸收居群形成光栅；(2)染料的光致取向；(3)不可逆的光致化学变化。由于每个光栅的衰减时间不同，在简并的四波混频配置下，通过关闭探针光束可以分别观察到：通常，相位共轭波的衰减时间以数量级增加(1)、(2)、(3)。对于杂蒽染料掺杂薄膜，相位共轭波的主要产生机制为：(1)和(3)；对于偶氮染料掺杂薄膜，相位共轭波的主要产生机制为(2)和(3)。然而。(3)是否有助于相共轭波的产生，取决于染料与基质的结合。例如，(3)在甲基红掺杂PMMA薄膜中起作用，而在甲基红掺杂半胱氨酸薄膜中不起作用。偶氮染料在泵浦波与探针波垂直极化的情况下，相共轭波的强度比在平行极化的情况下大20倍左右。

There has been some interest in optical phase conjugation with dye-doped ransparent polymer films. Some of xanthene and azo dyes have strong absorption at wavelengths of an argon-ion laser and also relatively long life times of their excited states, which make it possible to generate cw phase-conjugate waves at low intensities less than 0.5w/cm^2.Thick(10-100 m) and thin (<10 m) dye-doped polymer films were prepared by dip and spin-coating methods, respectively.Main mechanisms to produce phase-conjugate waves are due to the grating formation of (1) population by saturable absorption by dyes, (2) photo-induced orientation of dyes and (3) irreversible photo-induced chemical changes.As each grating has a different decay time, it can be separately observed by turning off a probe beam in a degenerate four-wave mixing configuration: In general, decay times of phase-conjugate waves increase in the order of magnitude.(1).(2)and(3).Dominant mechanisms of generation of phase-conjugate waves are (1) and (3) for xanthene-dye-doped films and (2) and (3) for azo-dye-doped films. However. whether (3) contributes to generation of phase conjugate waves or not, depends upon the combination of dyes and matrices. For example, (3) contributes to it in methylred-doped PMMA films but not in methylred-doped galatin films. It is very intersting that the intensity of phase conjugate wave by azo dyes are by about 20 times in the case of perpendicular polarization bet-ween pump and probe waves larger than in the case of parallel porarization.