Low-Loss RF Cavity for Quantum Cascade Laser Frequency Combs

Quantum cascade lasers (QLCs) are semiconductor devices, which are the dominant light source in the mid-IR part of the electromagnetic spectrum [1], and have recently been demonstrated to operate as frequency combs [2]. Characteristics of the comb operation are a broad, phase-locked optical spectrum of equidistant modes, and a strong narrow radio frequency (RF) beatnote, that is generated from the beating of those modes. One unique property of the QCL is the short upper-state lifetime, which allows the coupling between the injected current and the beatnote at the roundtrip frequency.