Two-color, intracavity pump-probe, cavity ringdown spectroscopy

Area of Science:

• Spectroscopy
• Cavity-Enhanced Techniques
• Trace Gas Detection

Background:

• Cavity Ringdown (CRD) spectroscopy is a sensitive technique for measuring trace gases.
• Existing CRD methods can be affected by drifts and spectral overlaps, limiting sensitivity and selectivity.
• Pump-probe schemes offer enhanced detection capabilities but require careful implementation.

Purpose of the Study:

• To demonstrate a proof-of-principle for intracavity pump-probe CRD detection.
• To develop a high-sensitivity and high-selectivity method for trace gas analysis.
• To overcome limitations of traditional CRD by compensating for background drifts and spectral interference.

Main Methods:

• Utilized a three-mirror, traveling-wave cavity for intracavity pump-probe CRD.
• Employed a two-color pump-probe scheme on N2O rovibrational transitions.
• Frequency-locked two quantum cascade lasers to specific cavity modes for high intracavity power and ringdown rates.

Main Results:

• Achieved immunity to empty-cavity ringdown drifts and spectral overlaps from non-target molecules.
• Demonstrated enhanced detection sensitivity through signal-averaging and background compensation.
• Successfully simulated two-color spectra using a density-matrix model under cavity resonance conditions.

Conclusions:

• Intracavity pump-probe CRD is a versatile and robust technique for trace detection.
• The method's background compensation enhances selectivity in complex spectral regions.
• The technique is particularly well-suited for mid-infrared trace gas analysis.