Gain measurements of scattering-assisted terahertz quantum cascade lasers

Using terahertz time-domain spectroscopy, the gain of scattering-assisted terahertz quantum cascade lasers is measured. By examining the intersubband gain and absorption over a wide range of bias voltages, we experimentally detect energy anticrossings—revealing information about the mechanism of laser action—and compare the resonant-tunneling injection scheme to the scatteringassisted injection scheme. The temperature performance of the gain medium is also measured and discussed, and an additional intersubband transition is identified that contributes to scatteringassisted lasing action at high temperatures. VC 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4732518]