Due to the long lifetime of indirect ͑interwell͒ excitons, exciton condensation ͑analogous to the Bose-Einstein condensation of bosons͒ is expected to occur in coupled quantum wells ͑CQW's͒. The critical conditions for the exciton condensation have been predicted to be strongly improved by high magnetic field perpendicular to the well plane. We present results of experimental study of transport and photoluminescence of indirect excitons in AlAs/GaAs CQW's at low temperatures (Tу350 mK͒ and high magnetic fields (B р14 T͒. Strong anomalies in the transport and luminescence of indirect excitons have been observed at low temperatures and high magnetic fields: a large increase of the exciton diffusivity, a large increase of the exciton radiative decay rate and a huge noise in the integrated exciton PL intensity. An interpretation of the observed anomalies as evidence of the exciton condensation ͑i.e., in terms of the onset of exciton superfluidity, superradiance of the exciton condensate, and fluctuations near the phase transition͒ is analyzed. The parameter ͑temperature, exciton density, and magnetic field͒ dependences of the observed anomalous transport and photoluminescence of indirect excitons show that these effects are consistent with the exciton condensation in the presence of a random potential. ͓S0163-1829͑98͒04827-9͔ I. INTRODUCTION: PROBLEM OF EXCITON CONDENSATION IN QUANTUM-WELL STRUCTURES

The ionization rates and subsequent electron dynamics for laser-induced plasma channels are measured for the noble gas series He, Ne, Ar, Kr, and Xe at 1.0 atm. The cw fluorescence emission increases superlinearly in the series from He to Xe in agreement with Ammosov-Delone-Krainov tunnel ionization calculations. The electron temperature after laser-induced plasma formation, measured by four-wave mixing, evolves from >20 eV to <1 eV kinetic energies with time constants ranging from 1 ns for He to 100 ps for Xe in agreement with an impact-ionization cooling model.

Coherent broadband radiation in the form of Rabi sidebands is observed when a ps probe laser propagates through a weakly ionized, electronically excited microplasma generated in the focus of an intense pump beam. The sidebands arise from the interaction of the probe beam with pairs of excited states of a constituent neutral atom via the probe-induced Rabi oscillation. Sideband shifting of >90 meV from the probe carrier frequency results in an effective bandwidth of 200 meV. The sidebands are controlled by the intensity and temporal profile of the probe pulse; with amplitude and shift in agreement with the predictions of a time-dependent generalized Rabi cycling model.