Mid-infrared absorption spectroscopy across a 14.4 THz 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 600 nm (14.4 THz or 480 cm(-1)) with around 3 nm (78 GHz or 2.6 cm(-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. (C) 2004 American Institute of Physics.