Pulsed and continuous-wave operation of long wavelength infrared (/spl lambda/=9.3 /spl mu/m) quantum cascade lasers

The operation of quantum cascade lasers at a wavelength (/spl lambda//spl sime/9.3 /spl mu/m) well within the 8-13-/spl mu/m atmospheric window is reported. A detailed study of intersubband luminescence in a vertical transition structure shows linewidths as narrow as /spl sim/10 meV at cryogenic temperatures, increasing to 20 meV at room temperature. Pulsed operation is demonstrated up to 220 K with a peak power /spl ap/10 mW and /spl ap/35 mW at 140 K. The temperature dependence of the threshold current density (J/sub th/) is described by a high T/sub 0/ (128 K), J/sub th/ is also systematically studied as a function of cavity length to determine the peak gain and waveguide losses. Continuous-wave, single-mode operation is demonstrated up to 30 K with powers /spl ap/2 mW.