Dual-Comb Interferometry for Coherence Analysis of Tightly Locked Mid-Infrared Quantum Cascade Laser Frequency Combs

Frequency combs are powerful tools for many applications and high performances are achieved by stabilizing these lasers. For operation in the mid-infrared, quantum cascade lasers (QCL) are ideal candidates as they present numerous advantages. However, stabilized QCL-combs lack a detailed characterization of their noise properties due to the sensitivity limits of current analyzing techniques. To overcome these challenges, what is believed to be the first tightly locked dual QCL-comb system is developed. Its use is twofold. First, phase noise analysis of the dual-comb signal shows residual phase noise below 600 mrad for all comb lines, and the comb coherence as well as the performances of the repetition frequency locking mechanism is characterized. Second, coherent averaging with a 7 x 105 Hz1/2 figure-of-merit system is demonstrated, which is compatible with high-precision spectroscopy. A tightly locked dual-comb system based on quantum cascade lasers operating in the mid-infrared is designed for a detailed characterization of the lasers noise properties. The coherence of the system as well as the performances of the repetition frequency locking mechanism are investigated, and coherent averaging is also demonstrated toward high-resolution spectroscopy. image (c) 2024 WILEY-VCH GmbH