Phase-shift cavity ring-down spectroscopy using mid-IR light from a difference frequency generation PPLN waveguide

Approximately 200 μW of mid-infrared (mid-IR) light around 3081 cm−1, produced by difference frequency generation (DFG) in a periodically poled lithium niobate crystal waveguide, has been used for phase-shift cavity ring-down spectroscopy measurements. The overlapping C122H4PR0(14) and RP6(10) and C12H2C13H2QP3(10) rotational lines of the ν9 fundamental ethene vibrational band at 3081.0016 cm−1 were probed in proof-of-principle experiments, and ethene detection was demonstrated with a minimum absorption coefficient of 1.4×10−7 cm−1 (∼4 min acquisition time). The compact DFG system, with a >35 cm−1 tuning range, has a considerable potential for use in trace gas detection and in molecular spectroscopy.