Quantum cascade laser frequency combs: physics and applications

Abstract

The quantum cascade laser has demonstrated the ability to provide gain over a very broad wavelength range, and has found many applications for sensing based on arrays of single frequency lasers or as external cavity lasers. Recently, we have shown that such broadband devices, when operated in continuous wave, emit as a coherent optical comb in which the phase relation between the comb modes corresponds approximately to a FM modulated laser. The important role of controlling the dispersion in the mid-infrared devices was shown also theoretically by using a Maxwell-Bloch formalism. In effect, by measuring the group delay dispersion (GDD) of the device and correcting for it using dedicated coatings, record power levels (120mW) with bandwidth approaching 100cm−1, together with excellent comb stabilities have been achieved. It has also recently shown that these combs can also be produced in the THz region of the spectrum, with the gain bandwidth covering a full octave. These new comb lasers enables the fabrication of a dual comb spectrometer based on a quantum cascade laser that offers a broadband, all solid-state spectrometer with no moving parts and a ultrafast acquisition time. We demonstrate a spectrometer and its first proof-of-principle applications, as well as new integrated dual-comb devices.