Professor Benjamin Williams’ group, in collaboration with Professor Mitchell Spearrin of UCLA MAE, has demonstrated that a new frequency-agile architecture for THz quantum-cascade lasers – the metasurface vertical-external-cavity surface-emitting-laser (VECSEL) – is well suited for terahertz (THz) gas-phase spectroscopy. The THz range is a spectral fingerprint range for many polar molecules, and often has stronger signatures than in the infrared or visible range. Laser absorption spectroscopy has been a workhorse technique in the IR/visible but has been little used in the THz due to lack of widely tunable sources. The metasurface VECSEL is coarsely tuned using a piezoelectric control over the 2.5-2.8 THz range to be close to the spectral features of interest, where it can then be finely swept over a range of 40-80 GHz to resolve multiple spectral features of gas-phase hydrogen sulfide (H 2 S). The relatively high power of the VECSEL source (~0.5 mW) allowed the use of room-temperature THz detectors, instead of cryogenic bolometers previously used in many THz laser absorption spectroscopy experiments.