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

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.