Em. Goldys et al., Signatures of excitonic dark states in the time-resolved coherent responseof a quantum well microcavity, PHYS REV B, 61(15), 2000, pp. 10346-10360
We study the coherent time-resolved response of a semiconductor microcavity
excited by an ultrashort light pulse. The cavity contains embedded quantum
wells and quantum well excitons an strongly coupled to cavity photons. Two
experimental situations are examined. We describe a linear regime when the
exciting light pulse is weak. Further, a low-temperature pump-and-probe ex
periment in a nonlinear regime is analyzed, with a cw pump beam circularly
polarized opposite to a weak ultrashort probe pulse in conditions yielding
a bipolariton-mediated optical Stark effect. In both cases we examine the r
esponse of a single quantum well and contrast it with that of several quant
um wells. In the latter case light is coupled only to a symmetric linear co
mbination (bright exciton) of excitonic states in individual quantum wells.
We find distinctive fingerprints of other linear combinations of exciton s
tates (dark excitons). In the linear regime, in addition to a pattern of Ra
bi oscillations between the two polariton states, additional beating freque
ncies appear, related to dark states. In the nonlinear case, the bipolarito
n formalism outlined by Ivanov et al. [Phys. Rev. B 52, 11 017 (1995)] allo
ws one to deduce a similar additional beating frequency and a splitting of
bipolariton frequencies related to their dark or bright state character. Th
is work identifies the effect of the microcavity parameters on its coherent
response and determines the experimental conditions in which the influence
of dark states may be observed.