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Updated: Jan 2, 2026

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing
Published on: March 22, 2019
Off-Axis Cavity-Enhanced Absorption Spectroscopy of 14NH3 in Air Using a Gain-Switched Frequency Comb at 1.514 μm
Satheesh Chandran1, Albert A Ruth1, Eamonn P Martin2
1Physics Department & Environmental Research Institute, University College Cork, Cork, Ireland.
Abstract:
A custom-designed gain-switched frequency comb (GSFC) source was passively coupled to a medium finesse (F ≈ 522) cavity in off-axis configuration for the detection of ammonia (14NH3) in static dry air. The absorption of ammonia was detected in the near infrared spectral region between 6604 and 6607 cm-1 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 NH3 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.
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