We report on the optical response of a semiconductor microcavity featuring a strong exciton–photon coupling. The weak excitation regime is investigated experimentally by means of time-resolved transmission and four-wave mixing experiments. The influence of electronic disorder on the coherent exciton–photon dynamics is discussed in terms of the solutions of the Maxwell-Bloch equations. The high excitation regime is investigated by using transient sub-picosecond pump–probe experiments. Optical amplification of the probe beam (up to a factor of five), as well as a fundamental change of the optical spectra, have been found close to and above the exciton saturation density. The observed oscillations are corresponding to the Rabi frequency of the excitons in the pump field.
We report on the optical response of a semiconductor microcavity featuring a strong exciton–photon coupling. The weak excitation regime is investigated experimentally by means of time-resolved transmission and four-wave mixing experiments. The influence of electronic disorder on the coherent exciton–photon dynamics is discussed in terms of the solutions of the Maxwell-Bloch equations. The high excitation regime is investigated by using transient sub-picosecond pump–probe experiments. Optical amplification of the probe beam (up to a factor of five), as well as a fundamental change of the optical spectra, have been found close to and above the exciton saturation density. The observed oscillations are corresponding to the Rabi frequency of the excitons in the pump field.
We investigate a GaAs/(Ga,Al)As Fabry-P\'erot microcavity, into which (In,Ga)As quantum wells have been inserted. The cavity is wedge shaped, i.e., the detuning between the bare-exciton resonance and the bare optical cavity mode depends on the spatial position on the sample. Linear transmission spectra reveal a well-resolved Rabi splitting of 8 meV at resonance, an inhomogeneously broadened exciton transition of 4--5-meV width, and an 0.7-meV-wide Fabry-P\'erot mode. The time-resolved transmission exhibits deep beatings and a subpicosecond exponential decay: a behavior similar to that foreseen in the strong-coupling regime and in the absence of electronic disorder. Conversely, the four-wave mixing response appears weakly influenced by the cavity and not much different from what is expected for bare excitons. A photon echo, dephasing times as long as 50 ps, and only weak Rabi oscillations are observed. The experimentally observed features can be explained by a model based on the numerical solutions of the Maxwell-Bloch equations. This model confirms the dramatic influence structural disorder in the quantum wells has on the coherent nonlinear exciton-photon dynamics.
Summary form only given. Optical interactions in semiconductor microcavities embedded with quantum wells enter a nonperturbative regime when the dipole coupling rate between the exciton and the cavity mode exceeds relevant decay rates. In this regime, coherent energy exchange between the exciton and the cavity mode, i.e. normal mode oscillation (NMO), takes place when the cavity mode is excited impulsively by a short laser pulse. Similar coherent oscillations have also been observed in transient four-wave mixing (FWM) responses. In this paper, we present experimental and theoretical studies on the nature of oscillations in these transient FWM responses. We show that, in contrast to earlier beliefs, oscillations in time-integrated transient FWM do not correspond to NMO of the exciton or photon populations. Theoretical studies further reveal that FWM arising from different physical mechanisms including band filling, excitation-induced dephasing, and renormalized electric fields is characterized by highly distinct coherent dynamics. Oscillations in transient FWM reflect interference between these coherent optical processes and can be used as a unique probe for exciton many-body interactions in the nonperturbative regime.
We report experimental and theoretical studies of the transient nonlinear response from semiconductor microcavities. We show that, in the nonperturbative regime, oscillations in time-integrated transient four-wave mixing do not correspond to normal mode oscillations of either the exciton or photon population in the cavity. Coherent nonlinear responses arising from band filling, excitation-induced dephasing, and renormalized electric fields feature highly distinctive dynamical behaviors. Coherent dynamics in transient four-wave mixing reflects interference between these nonlinear processes.
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 are 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 experiment 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 response of a single quantum well and contrast it with that of several quantum wells. In the latter case light is coupled only to a symmetric linear combination (bright exciton) of excitonic states in individual quantum wells. We find distinctive fingerprints of other linear combinations of exciton states (dark excitons). In the linear regime, in addition to a pattern of Rabi oscillations between the two polariton states, additional beating frequencies appear, related to dark states. In the nonlinear case, the bipolariton formalism outlined by Ivanov et al. [Phys. Rev. B 52, 11 017 (1995)] allows one to deduce a similar additional beating frequency and a splitting of bipolariton frequencies related to their dark or bright state character. This 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.
Recent progress in vertical surface-emitting-laser-diode technology has raised considerable interest in cavity-QED effects in high-quality vertical semiconductor microcavities. When an excitonic transition and a single cavity mode are strongly coupled, the normal modes of the system are coupled modes split by the vacuum-Rabi frequency, corresponding in the time domain to an oscillation of the excitation between modes of exciton and photon character. Recently, the vacuum-Rabi splitting and preliminary observations of time-domain oscillation in semiconductor quantum microcavities have been reported.1,2 In this paper we investigate rigorously the time-domain vacuum-Rabi oscillation by femtosecond upconversion and pump-probe techniques.
Recently, cavity quantum electrodynamic (QED) effects in semiconductor microcavities have been of considerable interest since, in the weak-coupling regime they play an important role in selectively increasing spontaneous emission into the lasing mode of vertical-cavity surface-emitting lasers (VCSEL’s) [1,2], enabling low-threshold, high speed, and high efficiency. In a strong-coupling regime, the normal modes of the coupled system are superpositions of the exciton and cavity modes. Hence the impulsively excited system will evolve in time with the energy oscillating between the exciton and cavity modes. This is known as a vacuum-Rabi oscillation (VRO), with a frequency of Ω=d¯⋅E¯/@@h, where d¯ is the transition dipole moment of atoms and E¯ the vacuum-field strength. Of course, VRO are observable only when the cavity lifetime and exciton dephasing time are long enough compared to VRO period. Recently, Weisbuch et al. [3] have reported an observation of the normal-mode vacuum Rabi splitting in 2-D-exciton/planar-DBR microcavities. The observed splittings were as large as 6 meV in reflection and transmission spectra, implying 690-fs vacuum Rabi oscillations.