Модель терагерцового квантово-каскадного лазера на основе двумерного плазмона

In this work, we calculated the characteristics of a two-dimensional plasmon amplified by an active medium based on a terahertz quantum-cascade structure. It is shown that for realistic parameters of GaAs/AlGaAs structures with quantum wells (mobility 2×105 cm2V-1s-1 at an electron concentration of 5×1011 cm-2 and at temperatures up to 77 K), the gain of a two-dimensional plasmon can reach 1500 cm-1 for frequency 2.3 THz. In addition, due to the strong localization of the plasmon electric field near the quantum well, only a few cascades of the active medium are required for amplification.

Two-dimensional spectroscopy on a THz quantum cascade structure

Understanding and controlling the nonlinear optical properties and coherent quantum evolution of complex multilevel systems out of equilibrium is essential for the new semiconductor device generation. In this work, we investigate the nonlinear system properties of an unbiased quantum cascade structure by performing two-dimensional THz spectroscopy. We study the time-resolved coherent quantum evolution after it is driven far from equilibrium by strong THz pulses and demonstrate the existence of multiple nonlinear signals originating from the engineered subbands and find the lifetimes of those states to be in the order of 4–8 ps. Moreover, we observe a coherent population exchange among the first four intersubband levels during the relaxation, which have been confirmed with our simulation. We model the experimental results with a time-resolved density matrix based on the master equation in Lindblad form, including both coherent and incoherent transitions between all density matrix elements. This allows us to replicate qualitatively the experimental observations and provides access to their microscopic origin.

An electrically pumped phonon-polariton laser

We report a device that provides coherent emission of phonon polaritons, a mixed state between photons and optical phonons in an ionic crystal. An electrically pumped GaInAs/AlInAs quantum cascade structure provides intersubband gain into the polariton mode at λ = 26.3 μm, allowing self-oscillations close to the longitudinal optical phonon energy of AlAs. Because of the large computed phonon fraction of the polariton of 65%, the emission appears directly on a Raman spectrum measurement, exhibiting a Stokes and anti-Stokes component with the expected shift of 48 meV.