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AIP conference proceedings

Towards A Mid-Infrared Polaron Laser Using InAs/GaAs Self-Assembled Quantum Dots

S. Sauvage, P. Boucaud, F. Bras, G. Fishman, J.M. Ortéga, J.-M. Gérard, Gilles Patriarche, Aristide Lemaître

Published Jan 1, 2007• 0 citations
Publisher

Abstract

A three‐level scheme based on S‐P polaron intersublevel transitions in n‐doped InAs/GaAs self‐assembled quantum dots is proposed to obtain laser effect around 25 μm wavelength under optical pumping. The theoretical proposition is supported by the experimental knowledge of key input parameters: T1, T2, oscillator strenghs and polarizations. The intensity thresholds are predicted to be two orders of magnitude lower than for corresponding intersubband lasers and laser effect is expected to occur up to room temperature. The T2 dephasing time of the S‐P+ transition is measured by performing an optical Rabi oscillation experiment in resonance with the S‐P+ transition. We show that the non‐monotonous population dependence with pulse area and damping of the oscillation is only compatible with a T2∼5 ps dephasing time, one order of magnitude longer than in quantum wells and one order of magnitude shorter than the 45 ps relaxation time of the s‐p transition, demonstrating a non relaxation‐limited decoherence for the transition.

DOI
10.1063/1.2730224

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A three‐level scheme based on S‐P polaron intersublevel transitions in n‐doped InAs/GaAs self‐assembled quantum dots is proposed to obtain laser effect around 25 μm wavelength under optical pumping. The theoretical proposition is supported by the experimental knowledge of key input parameters: T1, T2, oscillator strenghs and polarizations. The intensity thresholds are predicted to be two orders of magnitude lower than for corresponding intersubband lasers and laser effect is expected to occur up to room temperature. The T2 dephasing time of the S‐P+ transition is measured by performing an optical Rabi oscillation experiment in resonance with the S‐P+ transition. We show that the non‐monotonous population dependence with pulse area and damping of the oscillation is only compatible with a T2∼5 ps dephasing time, one order of magnitude longer than in quantum wells and one order of magnitude shorter than the 45 ps relaxation time of the s‐p transition, demonstrating a non relaxation‐limited decoherence for the transition.
Abstract A three level scheme based on S–P polaron intersublevel transitions in n‐doped InAs/GaAs self‐assembled quantum dots is proposed to obtain laser effect around 25 µm wavelength under optical pumping. Temperature dependence of the optical gain is theoretically analysed. Lasing effect is expected up to 300 K. To probe the T 2 decoherence time, one of the key parameter driving the laser performances, an optical Rabi oscillation experiment is performed on the pumping transition. Transmission variation is measured as a function of the pump pulse area and modelled by 2‐level optical Bloch equations considering inhomogeneous contributions. We show that the non‐monotonous population dependence and damping of the oscillation is only compatible with a T 2 ∼ 5 ps dephasing time, one order of magnitude longer than in quantum wells and one order of magnitude shorter than the 45 ps relaxation time of the S–P transition, demonstrating a non relaxation‐limited decoherence for the transition. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
We have performed time-integrated degenerate four-wave mixing experiments in InAs/GaAs self-assembled quantum dots. The quantum dots are excited in resonance with an intersublevel transition between the valence states of the dots. The dephasing time T2{T}_{2}T2​ is deduced from the time dependence of the photon echo amplitude as a function of the delay between the two incident pulses. At low temperature, a dephasing time T2{T}_{2}T2​ of 15 ps is measured for a resonant excitation at 7.4 \ensuremath{\mu}m wavelength. This dephasing corresponds to an homogeneous broadening of the intersublevel transition of 87 \ensuremath{\mu}eV. The polarization decay time is much longer than the one observed for resonant intersubband excitations in quantum wells. The dephasing time of the intersublevel polarization exhibits only a weak temperature dependence, indicating that the dephasing is not dominated by phonon-assisted scattering mechanisms.
Abstract In this work femtosecond spectral hole burning spectroscopy is used to resonantly excite ground state excitons in an ensemble of self‐assembled InAs/GaAs quantum dots with a strong pump pulse. Two fundamental coherent nonlinear effects are observed with the aid of the intrinsic time‐ and frequency resolution of the setup: The low temperature Rabi oscillation of the two‐level system associated with the excitonic ground state transition and the observation of two‐photon absorption in the surrounding GaAs crystal matrix. The emergence of the latter effect also infers the existence of charged excitons in the nominally undoped QD sample, backed up by the observation of additional spectral holes next to the excitonic transitions. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
We investigate the dephasing mechanism of optically-induced exciton coherence in an ensemble of InAs self-assembled quantum dots (QDs) using a two-pulse photon-echo (PE) technique. The sample was fabricated on an InP (311)B substrate using strain compensation to control the emission wavelength. This technique also enabled us to fabricate a 150-layer stacked QD structure for enhancing the PE signal intensity. We show the measured decay time of PE signal intensity for resonant excitation of ground-state transition is extremely long, which corresponds to ultralong coherence times of excitons in our QDs. We confirmed that non-radiative population relaxation and pure dephasing are considerably smaller than the radiative relaxation at low temperature. Furthermore, we demonstrate the ultrafast coherent control of QD exciton polarization by changing the pulse areas (Rabi oscillations) in the PE experiment. We also propose a new scheme for implementing QD quantum memory by using the PE technique.
Abstract In a single self‐assembled InGaAs quantum dot, the one‐exciton ground‐state transition defines a two‐level system, which appears as an extremely narrow resonance of only a few μeV width. The resonant interaction of this two‐level system with cw laser fields can be studied in detail by photocurrent spectroscopy, revealing the fine structure of the excitonic ground state as well as the effects of nonlinear absorption and power broadening. For the case of pulsed laser fields and in the absence of decoherence, the two‐level system represents a qubit. Excitations with ps laser pulses result in qubit rotations, which appear as Rabi oscillations in photocurrent experiments. Double pulse experiments further allow us to infer the decoherence time and to perform coherent control on a two level system.
In this presentation, we observed the coherent optical nonlinear interaction of exciton in a single InAs/GaAs self-assembled QD by using coherent control technique at the wavelength 1127 nm, 4.2 K. Due to the large diameter of InAs QDs in the longer wavelength range, dipole moment of confined excitons is predicted to be large so that coherent optical interaction such as Rabi oscillation is expected to be observed. Large dipole moment is one of the most important criteria to realize strong interaction between photons and excitons in QDs.