Microcavity design for low threshold polariton condensation with   ultrashort optical pulse excitation
  We present a microcavity structure with a shifted photonic stop-band to enable efficient non-resonant injection of a polariton condensate with spectrally broad femtosecond pulses. The concept is demonstrated theoretically and confirmed experimentally for a planar GaAs/AlGaAs multilayer heterostructure pumped with ultrashort near-infrared pulses while photoluminescence is collected to monitor the optically injected polariton density. As the excitation wavelength is scanned, a regime of polariton condensation can be reached in our structure at a consistently lower fluence threshold than in a state-of-the-art conventional microcavity. Our microcavity design improves the polariton injection efficiency by a factor of 4, as compared to a conventional microcavity design, when broad excitation pulses are centered at a wavelength of 740 nm. Most remarkably, this improvement factor reaches 270 when the excitation wavelength is centered at 750 nm. 
C. Poellmann, U. Leierseder, E. Galopin, A. Lema\^itre, A. Amo, J.   Bloch, R. Huber, and J.-M. M\'enard
cond-mat.mes-hall physics.optics