Asymmetric angular emission in semiconductor microcavities

Savvidis, P. G.; Baumberg, Jeremy J.; Stevenson, R. M.; Skolnick, M. S.; Whittaker, D. M.; Roberts, J.S.

doi:10.1103/physrevb.62.r13278

Cited by 75 publications

(78 citation statements)

References 19 publications

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“…These experiments have been interpreted in terms of enhanced scattering of reservoir excitons into the emitting polariton modes. The origin of the enhancement has been attributed to bosonic stimulation due to final state occupation.More recently, great insight into the subject has been given by angle-resolved experiments under resonant excitation [5][6][7][8]. In this kind of experiments, polaritons are optically excited at a desired energy and momentum, allowing a direct control of the polariton dynamics.…”

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Parametric luminescence of microcavity polaritons

Schwendimann²,

2001

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The spectral and dispersive emission properties are analytically determined for the twodimensional system of exciton-polaritons in microcavities excited by a resonant and coherent optical pump. New collective excitations result from the anomalous coupling between one generic polariton state and its idler, created by the scattering of two pumped polaritons. The corresponding parametric correlation is stimulated by the emitter and idler populations and drives very efficiently the luminescence. The intrinsic properties of the collective excitations determine a peculiar emission pattern.In their pioneering experiments, Weisbuch et al.[1] discovered a new kind of two-dimensional quasi-particles, resulting from the strong coupling between quantum well excitons and confined photons in a semiconductor microcavity. These peculiar particles, called microcavity polaritons, have a very sharp dispersion due to the very light mass of the cavity photon. Remarkably, this represents a condensed matter system of small mass quasiparticles which can be manipulated through laser beams both in frequency and momentum space. In principle, the low polariton density of states could allow large occupation numbers at relatively small densities of particles , well below the critical saturation value due to the fermionic nonlinearities. In other words, the polariton system could exhibit bosonic properties [2]. Furthermore, unlike unbound electron-hole pairs in ordinary semiconductor lasers, microcavity polaritons have a relatively short time of recombination into external photons. All these ingredients are indeed very promising for applications in the domain of ultrafast all-optical switching and amplification.Recently, Dang et al.[3] measured photoluminescence spectra from a II-VI microcavity excited with a nonresonant pump. A threshold was observed in the dependence of the polariton luminescence intensity as a function of the input power. Similar results were reported by Senellart and Bloch in a III-V microcavity [4]. These experiments have been interpreted in terms of enhanced scattering of reservoir excitons into the emitting polariton modes. The origin of the enhancement has been attributed to bosonic stimulation due to final state occupation.More recently, great insight into the subject has been given by angle-resolved experiments under resonant excitation [5][6][7][8]. In this kind of experiments, polaritons are optically excited at a desired energy and momentum, allowing a direct control of the polariton dynamics. In particular, Savvidis et al. [5] have uncovered a new kind of polariton parametric amplifier through pump-probe experiments. The angular selection rules for the parametric conversion of pumped polaritons into the probe and idler modes are unambiguously given by the energy and momentum conservation for the polariton scattering. In the case of an applied probe, the nonlinearity can be explained in terms of phase-matched wave-mixing of polariton matter beams [9]. Remarkably, giant nonlinearities occur also when the probe bea...

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Parametric luminescence of microcavity polaritons

Schwendimann²,

2001

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“…It also demonstrates that exciton-exciton collisions in semiconductors can be controlled and engineered to produce almost decoherence-free collisions for the realization of all-optical microscopic devices. DOI: 10.1103 The phase-coherent amplification of light-matter waves (cavity polaritons) recently observed is one of the most exciting developments in the field of semiconductor nonlinear optics [1][2][3][4][5][6][7]. It operates with analogous principles (but under very different conditions) of matterwave amplifiers based on ultracold atoms [8,9].…”

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Many-Body and Correlation Effects on Parametric Polariton Amplification in Semiconductor Microcavities

2003

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The complexity induced by the Coulomb interaction between electrons determines the noninstantaneous character of exciton-exciton collisions. We show that the exciton-photon coupling in semiconductor microcavities is able to alter the exciton dynamics during collisions strongly affecting the effective scattering rates. Our analysis clarifies the origin of the great enhancement of parametric gain observed when increasing the polariton splitting. It also demonstrates that exciton-exciton collisions in semiconductors can be controlled and engineered to produce almost decoherence-free collisions for the realization of all-optical microscopic devices. DOI: 10.1103 The phase-coherent amplification of light-matter waves (cavity polaritons) recently observed is one of the most exciting developments in the field of semiconductor nonlinear optics [1][2][3][4][5][6][7]. It operates with analogous principles (but under very different conditions) of matterwave amplifiers based on ultracold atoms [8,9]. Very recently it has been shown that a semiconductor microcavity (SMC) can amplify (via phase-coherent amplification of polaritons) a weak light pulse more than 5000 times [7].Cavity polaritons are two-dimensional eigenstates of SMCs which result from the strong resonant coupling between cavity-photon modes and two-dimensional excitons in embedded quantum wells (QWs) [10]. The dynamics and hence the resulting energy bands of these mixed quasiparticles are highly distorted with respect to those of bare excitons and cavity photons (Fig. 1). The exciton-photon coupling rate V determines the splitting (2V) between the two polariton energy bands. Coherent amplification of polaritons requires a coupling mechanism able to transfer polaritons from a reservoir (in this case provided by polaritons resonantly excited by a pump laser pulse on the lower polariton dispersion) to the signal mode, while conserving energy and momentum. Polaritons of different modes are coupled via their excitonic content, the coupling being provided mainly by the Coulomb interaction between excitons (also the anharmonic part of the exciton-photon interaction contributes). The microscopic theory of parametric polariton amplification [11] shows that the resulting Coulomb coupling strength is given by the exciton-exciton (XX) scattering rate [12] V XX ' 1:52E b a 2 0 (E b is the exciton binding energy and a 0 is the exciton Bohr radius) times the exciton fraction of the interacting polariton modes. This effective polariton-polariton interaction scatters a pair of pump polaritons into the lowest-energy state and into a higher-energy state (usually known as the idler mode). Energy and momentum conservation requires 2! k ! 0 ! 2k , where ! k is the energy of a pump polariton injected with an in-plane wave vector k as shown in Fig. 1. The scattering process is stimulated by a weak signal beam injected perpendicular to the cavity (k 0) that is thus greatly amplified. It has recently been shown that increasing the exciton-photon coupling V by inserting a large number...

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“…When the two probe pulses are in antiphase, the emission in the probe direction is strongly reduced and the polaritons at the pump angle decay spontaneously, as in the absence of an external seed, when the parametric scattering can be started by the few pump polaritons that relax into the band bottom, generating an emission around the normal direction [6,[18][19][20]. For the measurements in Fig.…”

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Coherent Control of Polariton Parametric Scattering in Semiconductor Microcavities

et al. 2003

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In a pump-probe experiment, we have been able to control, with phase-locked probe pulses, the ultrafast nonlinear optical emission of a semiconductor microcavity, arising from polariton parametric amplification. This evidences the coherence of the polariton population near k 0, even for delays much longer than the pulse width. The control of a large population at k 0 is possible although the probe pulses are much weaker than the large polarization they control. With rising pump power the dynamics of the scattering get faster. Just above threshold the parametric scattering process shows unexpected long coherence times, whereas when pump power is risen the contrast decays due to a significant pump reservoir depletion. The weak pulses at normal incidence control the whole angular emission pattern of the microcavity. In the past few years, microcavities working in the strong coupling regime have attracted quite a lot of attention [1][2][3]. The excitonic transition of the embedded quantum well is strongly coupled to the cavity photon mode. In the radiative region near k 0 the resonant exciton and photon modes split and give rise to composite bosons, the so-called microcavity polaritons [4]. The dispersion of the lower polariton (LP) strongly deviates from the unperturbed exciton dispersion. The particular shape of the lower polariton dispersion allows for a parametric polariton scattering process conserving energy and in-plane momentum [2,5,6]. Two polaritons with an in-plane momentum k p scatter into a signal-idler pair with zero and 2k p momenta. The microcavity can thus be understood as an optical parametric oscillator.It is well-known that the parametric oscillation in a classical optical parametric oscillator (OPO) is a fully coherent process. The crystal is pumped in the transparency region and the coherence time of the process is given by the duration of the pump pulses. The pump intensity required to achieve parametric oscillation is very high because the involved electronic states are virtual [7,8]. The semiconductor microcavity system exhibits three major differences to the classical OPO. First, the signal, pump, and idler states are real and thus very efficiently coupled to external laser light. Second, the excitations are interacting via a real Coulomb interaction which results in high parametric scattering rates. These two features illustrate the high efficiency of the process [2,5,6]. The third difference is that for our system the coherence time should not be given by the external laser pulses but by the properties of the excitations and the scattering themselves. The coherent control technique allows one to sense these coherence properties and to manipulate the scattering within its coherence time [9][10][11].In this Letter we report the coherent control of the parametric polariton scattering. The dynamics of the parametric scattering are governed by the lifetime of the real polariton states and the applied pump power [12]. Especially just above threshold the dynamics of the polariton scattering are ...

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Asymmetric angular emission in semiconductor microcavities

Cited by 75 publications

References 19 publications

Parametric luminescence of microcavity polaritons

Parametric luminescence of microcavity polaritons

Many-Body and Correlation Effects on Parametric Polariton Amplification in Semiconductor Microcavities

Coherent Control of Polariton Parametric Scattering in Semiconductor Microcavities

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