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Cavity polaritons
Semiconductor microcavities are composed of two Bragg mirrors embedding the cavity layer which contains
quantum wells. The cavity is designed so that the excitons confined in the quantum wells emit light at an energy
very close to that of the cavity mode. If the cavity finesse is large enough, photons emitted by the quantum well can oscillate
long enough within the cavity to be reabsorbed, re-emitted again and so on. The system enters the so-called strong coupling regime.
In this regime the eigenstates governing the physicl properties of the system are exciton-photon mixed states, named cavity polaritons, which present
very specific dispersion relations (see fig. 1b).
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Figure 1: a) Typical cavity structure to reach the exciton-photon strong coupling regime; b) Dispersion of the exciton and cavity photon,
as well as that of polariton states (in red).
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The lower polariton branch present a very reduced effective mass (as compared to the bare exciton) and obeys to bosonic statistics.
This is why semiconductor systems are a model system to study Bose condensation. Moreover polaritons interact efficiently with their environment.
As a result, semiconductor microcavities present enhanced non-linear properties.
The lower polariton effective mass can be changed by tuning the cavity mode energy with respect to that of the exciton.
This is evidenced in the angle resolved measurements presented below where polariton dispersions are directly observed.
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Figure 2 : Angle resolved photoluminescence measured on a planar cavity for three exciton-photon detunings.
Polariton states can be directly probed in such experiments.
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