Abstract

Degenerate four-wave mixing (DFWM) in disodium-fluorescein-doped glass revealed a large third-order susceptibility and a slow decay of the gratings that were responsible for optical phase conjugation. To understand the mechanisms for this, the following experiments were performed. The phase-conjugate signal in a DFWM setup was recorded for several concentrations of the dye in the glass. An Ar⁺ laser beam (488 and 457.9 nm) was used. Transient gratings were formed by turning the writing beams for the Ar⁺ laser on and off, and the decay was read by a He-Ne laser beam. Analysis showed that there are two exponential decays, 0.1 and 0.3 s, independent of the concentration. The possible presence of a thermal grating was eliminated by recording the decay times at 13° and 114°; we found no angular dependence. The decay time and the spectrum of the phosphorescence resulting from excitation by the Ar⁺ lines were recorded for the same samples. The analysis again showed two decay times, and the spectrum recorded with a double mono-chromator showed a structure having two peaks. It is therefore concluded that tripletstate gratings are responsible for the phase conjugation. However, the grating decay times were less than the phosphorescence decay times. Further investigations to understand this discrepancy are in progress.

© 1990 Optical Society of America