Exciton saturation in room temperature GaAs/AlGaAs multiple quantum wells

Holden, Todd; Kennedy, G. T.; Cameron, A. R.; Riblet, P.; Miller, A.

doi:10.1063/1.119694

Cited by 19 publications

(12 citation statements)

References 10 publications

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“…9 The operation and optimization of these devices rely on an understanding of the mechanisms that contribute to bleaching of the exciton absorption feature at room temperature. Previous work has shown that the relative contributions of the various mechanisms which cause bleaching can be distinguished by the use of circularly polarized light 10,11 and different laser pulse widths 12 in pump-probe measurements. This article describes pump-probe measurements in GaAs/AlGaAs MQWs using both picosecond and femtosecond duration pulses, as a function of wavelength, polarization, bandwidth, carrier density, and well width in order to quantify the individual contributions to excitonic optical nonlinearities.…”

Section: Introductionmentioning

confidence: 99%

Exciton saturation in GaAs multiple quantum wells at room temperature

Miller

Riblet

Mazilu

et al. 1999

Journal of Applied Physics

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Pump-probe experiments in GaAs/AlGaAs multiple quantum well samples are described using both picosecond and femtosecond laser pulses in different polarization configurations. The excitonic and free carrier components of exciton absorption saturation were analyzed as a function of well width. The relative importance of phase space filling, Coulomb screening and broadening contributions was determined from polarization and laser bandwidth dependencies via spin-dependent and spin-independent components. A five-level model was used to fit the data and nonlinear coefficients for the individual contributions were determined for each well width. The Coulomb contributions arising from screening and broadening of the excitons was found to dominate the absorption bleaching using picosecond pulses, whereas phase space filling was largest in the femtosecond regime. Exciton phase space filling was found to be four times larger than free carrier phase space filling at narrower well widths. A sublinear dependence of exciton broadening with carrier density was observed.

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Section: Introductionmentioning

confidence: 99%

Exciton saturation in GaAs multiple quantum wells at room temperature

Miller

Riblet

Mazilu

et al. 1999

Journal of Applied Physics

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“…The blueshift of the condensate increases linearly with the pumping intensity, in the case of ring-like excitation, showing the linear increase of the mean number of condensed polaritons. In the case of Gaussian excitation, the blue shift is strongly affected by the reservoir: it is twice as large as in the ring-excitation case and slowly saturates above threshold, indicating that exciton saturation has been reached [29].…”

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confidence: 99%

Polariton condensation in an optically induced two-dimensional potential

et al. 2013

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We demonstrate experimentally the condensation of exciton-polaritons through optical trapping. The non-resonant pump profile is shaped into a ring and projected to a high quality factor microcavity where it forms a 2D repulsive optical potential originating from the interactions of polaritons with the excitonic reservoir. Increasing the population of particles in the trap eventually leads to the emergence of a confined polariton condensate that is spatially decoupled from the decoherence inducing reservoir, before any build up of coherence on the excitation region. In a reference experiment, where the trapping mechanism is switched off by changing the excitation intensity profile, polariton condensation takes place for excitation densities more than two times higher and the resulting condensate is subject to a much stronger dephasing and depletion processes.Strong coupling of cavity photons and quantum-well excitons gives rise to mixed light-matter bosonic quasiparticles called exciton-polaritons or polaritons [1]. Due to their photonic component, polaritons are several orders of magnitude lighter than atoms, which makes their condensation attainable at higher temperatures [2,3]. The manifestations of polariton condensation include polariton lasing [4], long-range spatial coherence [5,6] and stochastic vector polarisation [7]. In an ideal infinite twodimensional cavity the polariton gas is expected to undergo the Berezinsky-Kosterlitz-Thouless (BKT) phase transition [8], while in realistic structures, polaritons can condense in traps induced by random optical disorder [2] or mechanically created potentials [3,9]. Polariton condensation has also been observed in structures of lower dimensionality [10][11][12][13] where the structure itself acts as the trapping potential. Furthermore, the manipulation of polariton condensates by optically generated potentials has been previously shown [14][15][16]. In these works the condensation process was not assisted by the optical potential but used to localize an already formed polariton condensate.Here, we report on the first manifestation of polariton condensation assisted by an optically generated two dimensional potential. This scheme allows for the formation of a polariton condensate spatially separated from the excitation spot. Owing to the efficient trapping in the optical potential we observe a reduced excitation density threshold as well as higher coherence due to the decoupling of the condensate from the exciton reservoir. Polariton condensation prior to the build-up of coherence in the form of photon or polariton lasing [17,18] at the excitation area on the sample, decisively resolves the debate on the phase relation between the excitation laser and polariton condensate.We used a high quality factor GaAs/AlGaAs microcavity containing four separate triplets of 10 nm GaAs quantum wells and has a vacuum Rabi splitting of 9 meV [19], held at ∼ 6.5 K in a cold-finger cryostat and excited non-resonantly at the first reflection minimum above the cavity stop band with a s...

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“…At ⌬t ϳ 0 ps, both I dt ͑ Ϯ ͒ increases due to the spin-independent CS. 11 The difference between I dt ͑ + ͒ and I dt ͑ − ͒ is seen up to ⌬t ϳ 350 ps. In Fig.…”

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confidence: 96%

“…2 In this context, optical nonlinearity and circular dichroism induced by spin-polarized electrons or excitons are important and essential. Recently, many experiments of time-resolved optical spectroscopy have explored exciton [3][4][5][6][7] and spin [8][9][10][11] dynamics in semiconductors and their quantum structures in depth. The mechanisms responsible for modulation of exciton resonance absorption at low excitation levels and low temperatures are phase space filling ͑PSF͒ and Coulomb screening ͑CS͒ which can be separated into short-ranged exchange interaction and longranged Coulomb correlation between exciton-exciton and free electron-hole pairs.…”

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Intersubband exchange interaction induced by optically excited electron spins in GaAs/AlGaAs quantum wells

Morita

Sanada

Matsuzaka

et al. 2009

Applied Physics Letters

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Spin-dependent intersubband excitonic interactions have been investigated in GaAs/AlGaAs quantum wells by two-color pump and probe spectroscopy. We generated spin-polarized electrons in the lowest subband by resonant excitation of the heavy-hole exciton (E1-HH1) and observed polarization-dependent broadening of the second-subband exciton resonance (E2-HH2 and E2-LH1). The exchange interaction between the first and the second-subband excitons is found to play a crucial role in polarization-dependent spectral modulation as well as spin-independent Coulomb screening.

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Exciton saturation in room temperature GaAs/AlGaAs multiple quantum wells

Cited by 19 publications

References 10 publications

Exciton saturation in GaAs multiple quantum wells at room temperature

Exciton saturation in GaAs multiple quantum wells at room temperature

Polariton condensation in an optically induced two-dimensional potential

Intersubband exchange interaction induced by optically excited electron spins in GaAs/AlGaAs quantum wells

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