Thermally induced degenerate four-wave mixing

Time-dependent aspects of thermally stimulated degenerate four-wave mixing (DFWM) in absorbing liquid solutions have been theoretically investigated through a coupled electromagnetic-hydrodynamic theory originally formulated to study stimulated scattering processes. The various time scales involved in the interaction (including those characteristic of acoustic modes and thermalization effects) are identified and relevant laser and media parametrical relations are sorted out. Suitable approximation regimes are then outlined, corresponding to specific experimental situations of interest and allowing for relatively simple and tractable analytic relations to be derived. In particular, the effects of finite rise time of thermalization were studied and found to lead to a possibly strong angular dependence in the conjugate reflectivity. Acoustic modes and their influence on the process efficiency were also investigated. The calculations culminate in a set of guidelines for optimizing conjugation efficiencies, through judicious choice of dye-solvent combinations, "read" pump time delays, experimental arrangements, and laser pulse parameters.