Measurement and Analysis of Overlapping Ammonia Spectral Lines via Dual‐Comb Spectroscopy

Ammonia (NH₃) emissions pose significant hazards to both the environment and human health, making high‐precision monitoring of ambient NH₃ concentrations particularly crucial. In this study, a high‐precision NH₃ detection system was designed based on near‐infrared dual‐comb spectroscopy (DCS). A laser source with a central wavelength of 1531 nm is employed as the laser relay; by locking the relative frequencies of two optical combs to the relay laser separately, dual‐comb with a central frequency of 1531 nm, a repetition rate of 518.25 Hz, and an output power of 30 μW is generated. A multi‐pass gas absorption cell with a base length of 0.113 m and 250 reflections is utilized to achieve an effective optical path length of approximately 25 m. Under conditions of 296.15 K and 1 atm, three overlapping absorption lines at 6528.78 cm⁻¹, 6528.88 cm⁻¹, and 6529.18 cm⁻¹ of 1000 ppm NH₃ are detected, verifying the feasibility of high‐resolution dual‐comb spectroscopy for measuring overlapping spectral lines. Allan variance analysis is performed on the experimental data, yielding a minimum detection limit (MDL) of 0.00128 for absorbance at an integration time of 972 s, corresponding to a concentration MDL of ~2 ppm. This research provides technical insights for achieving high‐precision measurement and analysis of overlapping spectral lines.