Mid-infrared absorption spectroscopy across a 14.4THz spectral range using a broadband femtosecond optical parametric oscillator

We describe the implementation of optical absorption spectroscopy in which a Ti:sapphire pumped femtosecond optical parametric oscillator based on periodically poled lithium niobate was used as a broadband source to directly acquire a midinfrared absorption spectrum of methane gas. Fourier-transform spectroscopy was performed using the idler output from the optical parametric oscillator to directly acquire spectra spanning over 600nm (14.4THz or 480cm−1) with around 3nm (78GHz or 2.6cm−1) resolution. This approach combines the advantages of spectroscopy using broadband thermal sources with the high power and excellent beam quality of a mode-locked laser source.