Quantitative Modeling of Gain in Quantum Cascade Lasers under Operational Intensities

Abstract: This thesis adresses modeling of quantum cascade lasers using non-equilibrium Green’s functions. Focus lies on the quantitative modeling of the gain when the systems are exposed to strong laser fields, as under realistic opertional conditions. In the first part, an introduction to the general concepts is provided, together with a discussion on approximate analytic expressions. The second part consists of the six papers listed below. Paper I analyzes the temperature dependence of the gain and current of a terahertz quantum cascade laser.Paper II provides details of the implementiation of the non-equilibriun Green’s function formalism for simulations of transport in quantum cascade lasers.Paper III demonstrates a microscopic approach to simulate the second harmonic generation of a mid-IR quantum cascade laser. Paper IV documents the implementation of a rudimentary form of the GW-approximation for the electron-electron scattering self-energy.Paper V analyzes a proposed gain mechanism in superlattices, and presents an optimized structure plausible for laser operation.Paper VI shows simulation results of 16 samples from 5 different laboratories. From this systematic study, trends with repspect to the growth place are identified.