Detection and spectroscopy of OH fundamental vibrational band based on a difference frequency generator at 3 μm

We report the detection and spectroscopy of the fundamental vibrational band of the OH radical at 3 μm. The mid-IR radiation was produced by difference frequency generation mixing a Nd–YAG laser and a diode laser (λ=0.785 μm). OH detection was demonstrated at high sensitivity by observing a minimum detectable pressure of 0.225 μbar for an optical length of 50 cm. Finally, we identified four OH lines, belonging to two Λ-doublets, and measured their spectral positions with an accuracy of ≃1.6×10−3 cm−1.