Nonlinear gain behavior in injectorless quantum cascade lasers

The gain spectra of a continuous wave operating injectorless quantum cascade lasers are presented. These are extracted by the Hakki-Paoli method from electroluminescence measurements. The device operates around 7.4 m and has threshold current densities in pulsed and continuous wave operation at room temperature that measure 1.1 and 1.76 kA/cm², 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 compared with the 1/L threshold behavior versus temperature, indicating a nonlinear gain current dependence of injectorless devices.