Dispersion in a broadband terahertz quantum cascade laser

Abstract

We present dispersion data of a broadband terahertz quantum cascade laser with a heterogeneous active region. The experimental method to extract the group velocity dispersion of the entire laser cavity, including the contributions of the active region, the semiconductor material, and the waveguide relies on a time-domain spectroscopy system. The obtained group velocity dispersion curves exhibit oscillations with amplitudes up to 1 × 105 fs2/mm between 2.0 and 3.0 THz and strongly depend on the driving conditions of the laser. This indicates that the group velocity dispersion is mainly determined by the intersubband gain in the active region. The obtained dispersion data are compared to a dispersion model based on multiple Drude-Lorentz gain media yielding a significant correlation.