  A femtosecond mode-locked laser is used for the first time as a broadband
infrared source for high resolution Fourier transform absorption spectroscopy.
Demontration is made with a Cr^4+:YAG laser. The entire nu_1+nu_3
vibration-rotation band region of acetylene, observed after passing through a
single pass 80-cm long cell, is simultaneously recorded between 1480 and 1600
nm, in 7.9 s with a signal to noise ratio equal to 1000. Two hot bands of the
most abundant acetylene isotopologue and the n1+n3 band of the ^13C^12CH_2 are
also present. The noise equivalent absorption coefficient at one second
averaging is equal to 7 10^{-7} cm^{-1}.Hz^{-1/2} per spectral element.
