Optical control of comb emission in mid infrared quantum cascade lasers

Optical feedback and injection locking are two well established techniques allowing for the control of mid infrared quantum cascade lasers (QCLs) emission. The first one, with the laser mounted in an external cavity configuration [1], enables wide tunability of the source. On the other hand, the second one, implemented using a metrological-grade radiation as master [2], enables the transfer of the phase stability of the master oscillator to the QCL radiation. Recently, comb operation in QCLs has been demonstrated [3]. Although a phase relation between the modes has been demonstrated, the comb emission has to be stabilized to be used for high-resolution spectroscopy applications. Optical techniques seem to be good candidates to this task. This aspect will be discussed in detail