Variation of the emission frequency of a terahertz quantum cascade laser

Abstract

The variation of the emission frequency of a quantum cascade laser of the 3.2 THz range within a single radiation pulse was studied using high-resolution Fourier spectroscopy. A significant (108 MHz) increase in frequency in the first 4 μs of a pulse was found. This increase is attributed to a change in the electron part of permittivity of the laser active region coinciding with a rise in the emission intensity. The frequency dropped by 81 MHz in the following 40 μs of a radiation pulse due to a change in the lattice part of permittivity occurring as the laser active region was heated during a radiation pulse.