Generation of Frequency Combs by Quantum Cascade Lasers Emitting in the 8-μm Wavelength Range

Abstract

We have studied the generation of frequency combs by quantum cascade lasers (QCLs) emitting in the 8-μm wavelength range. Results showed the presence of a self-pulsation regime near the lasing threshold. Further increase in the pumping current led to a sharp increase in width of the lasing spectrum, which allowed us to obtain frequency combs with a spectral width exceeding 1.5 THz. This behavior of QCLs can be explained by radiation absorption at the stripe edge that is related to the penetration of waveguide mode into unpumped regions.