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

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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.