Coherent transient cyclotron emission from photoexcited GaAs

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Abstract
Femtosecond photoexcitation near, but above, the band gap in GaAs epitaxial layers and doped heterostructures in magnetic fields is shown to produce transient coherent cyclotron emission, lasting for several picoseconds at low temperatures. This emission reflects the relatively long phase relaxation of coherent electronic excitations associated with free electron inter-Landau-level transitions. In a doped, wide parabolic quantum well, the photoexcited carriers drive the magnetoplasmon mode of the equilibrium carriers, producing a dramatic resonance as the cyclotron frequency crosses the magnetoplasmon frequency.