Actively mode-locked pulses from a mid-IR quantum cascade laser

The discovery of short optical pulses has triggered various breakthroughs in fundamental science and technology. While mode-locked lasers emitting visible and near-infrared light have reached a high level of maturity, methods for the generation of pulses in the mid-infrared (mid-IR) region beyond 5 µm wavelength are mostly based on non-linear downconversion of near-infrared pulses. Nowadays, quantum cascade lasers (QCLs) have become the dominant laser source in the mid-IR region [4] . In contrast to most other types of lasers, both the upper state lifetime and the gain recovery time of mid-IR QCLs are considerably shorter than the cavity roundtrip period. These properties have proven to be a major obstacle for the formation of short pulses [1] .