Mid-infrared absorption spectroscopy of methane using a broadband femtosecond optical parametric oscillator based on aperiodically poled lithium niobate

We describe the implementation of optical absorption spectroscopy in which a Ti:sapphire pumped femtosecond optical parametric oscillator based on aperiodically poled lithium niobate was used as a broadband source to directly acquire a mid-infrared 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 600 nm (14.4 THz or 480 cm^-1) with around 2.2 nm (55 GHz or 1.9 cm^-1) resolution. Data are presented of absorption measurements in methane at pressures of 2 bar, 250 mbar and 25 mbar. This approach combines the advantages of spectroscopy using a broadband thermal source with the high power and excellent beam quality of a modelocked laser source. © 2005 IOP Publishing Ltd.