The first demonstration of direct femtosecond-pulse emission from a quantum cascade laser in the mid-infrared region paves the path towards novel applications of ultrashort laser pulses.
Lasers that emit light not as a continuous beam but in extremely short bursts — typically of picosecond (10–12 s) length or shorter — have transformed various fields of science and technology, from studying atomic and molecular processes at ‘ultrafast’ timescales to the precise delivery of highly concentrated amounts of energy for material processing and eye surgery. Versatile laser exist nowadays for many such applications in the visible to near-infrared range of frequencies. By contrast, devices at lower frequencies are often limited by relatively long pulse durations and low peak powers, and entail complex, bulky instrumentation. This might be about to change now, owing to an advance in the group of Prof. Jérôme Faist at the Institute for Quantum Electronics. Reporting in Nature Photonics, they demonstrate for the first time the generation of powerful femtosecond (10–15 s) pulses in the mid-infrared region. This is a frequency band of great practical interest, as it associated with the stretching, vibration and rotation of a broad range of molecules — earning it the name of ‘molecular fingerprint region’.