Off-Axis Cavity-Enhanced Absorption Spectroscopy of 14NH3 in Air Using a Gain-Switched Frequency Comb at 1.514 μm

摘要

A custom-designed gain-switched frequency comb (GSFC) source was passively coupled to a medium finesse ( ≈ 522) cavity in off-axis configuration for the detection of ammonia ( NH ) in static dry air. The absorption of ammonia was detected in the near infrared spectral region between 6604 and 6607 cm using a Fourier transform detection scheme. More than 30 lines of the GSFC output (free spectral range 2.5 GHz) overlapped with the strongest ro-vibrational ammonia absorption features in that spectral region. With the cavity in off-axis configuration, an NH detection limit of ∼3.7 ppmv in 20 s was accomplished in a laboratory environment. The experimental performance of the prototype spectrometer was characterized; advantages, drawbacks and the potential for future applications are discussed.