Synchrotron infrared transmission spectroscopy of a quantum cascade laser correlated to gain models

We measure the broadband optical gain and absorption spectra between 0.1 and 0.7 eV in a two-phonon resonance design quantum cascade laser, with the infrared beam of a synchrotron light source, and correlate them to established simulation models, based on the density matrix formalism, and on the non-equilibrium Green's function theory. We show that accounting for the distribution of carriers in momentum space improves the description of the high-energy absorption from the excited states located close to the active wells and results in an accurate prediction of the gain. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4774319]