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The magneto-optical Kerr and Faraday effect allows the monitoring
of spin dynamics in semiconductors with sub-picosecond time resolution
and with a spatial resolution that is limited only by the wavelength
of the probe beam. However, the effect is rather weak and typically
an ensemble of about  electron
spins is needed to obtain a reasonable signal-to-noise ratio. Here,
we investigate how the sensitivity of the Faraday rotation can be
improved by placing the semiconductor in an asymmetric Fabry-Perot
cavity. The essential idea is that, in a cavity, the probe beam
passes through the semiconductor several times (of the order of
the cavity Q factor). With each passage, the Faraday rotation is
added.
We have studied the signal enhancement in a GaAs quantum well embedded
in a microcavity consisting of AlAs/AlGaAs Bragg gratings, and obtained
the time-resolved dynamics of quantum well electrons with enhanced
signal strength as a function of the detuning between cavity and
exciton energy, the enhancement as well as the spectrum of the Faraday
signal changes [1]. We attribute these changes to a transition of
the cavity across the impedance-matching limit.
References
| [1] |
G. Salis and M. Moser, Phys. Rev. B 72, 115325
(2005). |
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