Time- and spectrally resolved reflectivity measurements on multiple-quantum-well structures excited by ultrashort laser pulses are presented. In Bragg structures, where the interwell distance amounts to half the optical wavelength at the exciton resonance, superradiant coupling of the polarization dynamics within different quantum wells leads to an enhancement of the reflectivity strength and linewidth. We show that the superradiance is not limited to the heavy-hole exciton but can be observed even on excited and light-hole exciton states as well as on correlated electron-hole pair states. These coupling effects grow with the number of quantum wells. For our samples containing 60 and 30 quantum wells, pronounced superradiant enhanced reflectivity is present even at high excitation intensities and high temperatures, showing the insensitivity of radiative coupling with respect to incoherent scattering processes. Our findings are in good agreement with solutions of the semiconductor Maxwell-Bloch equations.
|Original language||English (US)|
|Number of pages||7|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Sep 15 2000|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics