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Intracavity molecular spectroscopy in the mid-IR using ultra-broadband optical parametric oscillator

We have performed intracavity molecular spectroscopy of water vapor, isotopic carbon dioxide, methane, acetylene, carbon monoxide, formaldehyde and other gases using broadband mid-IR sync-pumped OPO sources (PPLN-based OPO pumped by a femtosecond Er-fiber laser, or OP-GaAs-based OPO pumped by a femtosecond Tm-fiber laser) operating near degeneracy, with up to 2.5–6.1 μm instantaneous bandwidth. We found that the measured spectral line shapes may show dispersive features. The measured spectra were compared to a simple model, based on the intracavity round-trip dispersion, and excellent agreement between theory and measurements was found. Detection limits in the ppb-range were demonstrated.