Nonlinear gain behavior in injectorless quantum cascade lasers

The gain spectra of a continuous wave operating injector- less quantum cascade lasers are presented. These are extracted by the Hakki-Paoli method from electroluminescence measurements. The device operates around 7.4 μm and has threshold current densities in pulsed and continuous wave operation at room temperature that measure 1.1 and 1.76 kA/cm 2 , respectively. The differential gain coefficients around 100 cm/kA at liquid nitrogen temperature and 44 cm/kA around room temperature are determined. The gain measurement values are com- pared with the 1/L threshold behavior versus temperature, indicating a nonlinear gain current dependence of injectorless devices. C 2010 Society of