Gain and losses in terahertz quantum cascade laser

The waveguide losses and the laser gain of a THz quantum cascade laser as a function of temperature and driving current are determined in this study by coupling broadband THz pulses into the laser's waveguide. Measurements are performed based on the bound-to-continuum design. Results show that at high temperatures the lasing operation in not only hampered by phonon/electron scattering but also by thermally activated absorption.