Terahertz Tri‐Comb Laser Sources

The recent advancement of tri‐comb spectroscopy provides significant benefits by employing three coherent frequency combs. This innovative technique eliminates mechanical moving parts while preserving comb resolution, and enhances measurement precision through an additional frequency‐sampling mechanism that resolves ambiguities inherent in conventional dual‐comb approaches. However, the development of tri‐comb systems operating in the terahertz (THz) range has been limited, primarily due to the scarcity of efficient THz light sources and high‐speed detectors. In this work, a THz tri‐comb laser source is presented utilizing three quantum cascade lasers (QCLs) operating at approximately 4.2 THz. Optical coupling among the lasers is investigated through 2D and 3D finite‐element simulations. Experimental demonstration of tri‐comb operation is conducted, with characterization of the down‐converted tri‐comb signals' frequency stability. The measured signals showed signal‐to‐noise ratios exceeding 30 dB and a sufficient number of spectral comb teeth to support spectroscopic measurements. By employing a self‐detection scheme, the tri‐comb system allows simultaneous acquisition of multiple spectra (obtained by beating any two of the three combs), reducing errors and improving measurement accuracy. The proposed THz tri‐comb laser source represents an advancement in high‐precision spectroscopic and metrological applications within the THz regime, offering a compact and robust solution for next‐generation sensing and measurement technologies.