[OPTICAL REVIEW Vol. 6, No. 6 (1999) 522-528]

Polarization-Dependent Phase-Conjugate Reflectivity in Randomly Oriented Saturable Absorbers: Effects of Direction of Transition Dipole Moment Associated with Excited-State Absorption

Tsutomu SATO and Shigeki MIYANAGA*

Department of Electrical and Electronic Engineering, Muroran Institute of Technology, 27-1, Mizumoto, Muroran, 050-8585 Japan

(Received April 30, 1999; Accepted July 21, 1999)

The effects of the direction of transition dipole moment on polarization-dependent phase-conjugate (PC) reflectivity by degenerate four-wave mixing in a saturable-dye-doped film are theoretically investigated. On the basis of a four-energy-level model for the saturable dyes, the pump-intensity dependence of the PC reflectivity is calculated for the two cases of a probe wave being polarized either parallel or perpendicular to pump waves, when the transition dipole moment associated with excited-state absorption tilts from that associated with ground-state one. For the parallel polarization, in the case of two transition dipole moments having different directions, a dip appears in the PC reflectivity curve near a resonant frequency on account of the characteristics of nonlinear absorption, whereas it disappears when the frequency of light is off resonance due to the influence of nonlinear refractive index.

Key words : saturable absorption, polarization-dependent phase-conjugate wave, degenerate four-wave mixing, excited-state absorption, saturable-dye-doped film, direction of transition dipole moment