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A significant enhancement in the mode locking of a KCl:Tl color-center laser has been observed when a length of optical fiber having positive group-velocity dispersion was incorporated within an external control cavity. Pulse durations of ~260 fsec were obtained by this method, representing a compression factor ~60x that with the colorcenter laser alone. Similar results have also been observed with an InGaAsP semiconductor diode amplifier as the nonlinear element within the control cavity.

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The transient grating technique is used to demonstrate how the temporal response of four-wave mixing in multiple-quantum-well structures depends on sample orientation. Variation of the decay times associated with the short-period grating in a phase-conjugate geometry between 40 and 500 psec is demonstrated in a GaAs/AlGaAs multiple-quantum-well structure and interpreted in terms of the large anisotropy in the carrier diffusion.