INFRARED-ABSORPTION SPECTROSCOPY USING A FREE-ELECTRON LASER

The spectral bandwidth of an infrared free-electron laser is rather br oad (greater than or equal to 10 cm(-1) FWHM) due to the short duratio n of the micropulse (1 ps). It is demonstrated that by resolving the t ransmitted laser beam using a spectrometer, it is possible to record I R spectra of gases that are limited in resolution only by that of the spectrometer. Over 20 air absorption lines (due to water vapor) are re corded over one free spectral range of the free-electron laser. As a f urther demonstration of the spectroscopic technique, an IR absorption spectrum for ammonia is recorded for two vibration-rotational transiti ons. (C) 1998 Elsevier Science B.V.