Abstract

We report what we believe to be the first observation of coherent transient absorption changes in glasses doped with quantum dots of CdS_0.12Se_0.88. These observations were made at room temperature with on-resonant laser pumping. We observe a transient bleaching on the high energy side of the pump center wavelength, and a transient absorption increase on the low energy side. The transient effects last for a time about equal to the pump pulse duration, 80 fsec, after which real carrier generation masks the effects. The results can be qualitatively explained by a spectral shift in the direction predicted by the optical Stark effect. This was a pump-probe experiment where the 622-nm pump center wavelength was on the long wavelength side of the lowest energy transition in the quantum dots but still well within the absorption band. The radii of the microcrystallites ranged from 20 to 40 Å, and T₂ in similar samples was estimated to be 60 fsec or less. Although the laser pulsewidth is longer than the dephasing time in the sample, we were still able to see coherent effects.

© 1991 Optical Society of America