Tailoring Risken-Nummedal-Graham-Haken instability in quantum cascade lasers

The multimode Risken-Nummedal-Graham-Haken (RNGH) instability in a CW laser arises due to Rabi splitting of the lasing transition induced by the lasing mode. Observation of large spectral broadening on the order of 2Ω Rabi provides an indication of multimode RNGH instability. Results of the experimental studies on RNGH instability in Mid-IR InGaAs/AlGaAs quantum cascade lasers (QCLs) operating at 8 μm wavelength are presented. This paper reports on steady-state and time-resolved spectral measurements and 2D order interferometric autocorrelation (IAC) measurements in free running QCLs and QCLs subjected to optical pumping and characterize it via spectral measurements and via 2D order interferometric autocorrelation (IAC) measurements. Results show that effect of applied bias field on the lasing transition, which can be controlled either with applied bias or optical excitation of free carriers on interband transition, can switch on and off broad multimode emission associated with RNGH instability.