REDUCED-BACKGROUND GAS-PHASE ABSORPTION-SPECTROSCOPY

We propose and demonstrate a new method for single-shot multiplex abso rption spectroscopy that permits enhanced sensitivity in the simultane ous measurement of multiple spectral lines in rapidly changing gas-pha se media, such as turbulent flames. It uses an ultrashort laser pulse that propagates through the absorbing medium, for which the relevant a bsorption information resides in the free-induction decay that is trai ling behind the transmitted pulse. Time gating out most of the transmi tted pulse, but not the free-induction decay, enhances the relative fr action of light that contains absorption information when the spectrum is measured. This procedure reduces the background associated with th e input light, thus enhancing detection sensitivity. (C) 1998 Optical Society of America.