Sub-Bandwidth Limited Time-Domain Signal in Mid-Infrared Quantum Cascade Lasers

Quantum cascade lasers (QCLs) offer an attractive platform for mid-infrared frequency combs, due to their compact, on chip geometry, emitting powers as high as 1 W at room-temperature [1–3]. A defining feature is their quasi-continuous intensity output, which is predominantly frequency modulated. To force the QCL into amplitude-modulated operation, active modelocking has been used to achieve pulses on the picosecond-scale [4] and external compression has yielded pulses close to the Fourier Limit at 630 fs [5]. For shorter length scales beyond the Fourier-limit, superoscillations, which are caused by the interference of the different Fourier components, offer great potential for use in ultrafast spectroscopic techniques [6], [7].