Laser-induced grating techniques for gas-phase excited-state spectroscopy

Laser-induced grating techniques are very sensitive for detecting optical transitions of excited-state molecules. Induced-grating methods have been widely employed for time-resolved studies, particularly in condensed phase. Recently, their application to spectroscopic studies of excited states in the gas phase has also been demonstrated. Laser-induced grating techniques have several advantages over other sensitive excited-state spectroscopic methods. Transitions are monitored by diffraction of a probe beam into a unique direction, thus providing background-free detection. Diffraction of the probe beam is sensitive to the induced absorption so, for example, transitions to nonfluorescent states can be observed. Two-color, laser-induced grating techniques have the additional advantage of only generating a signal when both frequencies are resonant, which can simplify interpretation of the spectra in some cases. This talk will give an overview of recent work in the application of laser-induced grating methods to gas-phase excited spectroscopy. Several examples that show the versatility of these techniques will be discussed, including experiments that detect excited state absorption, stimulated emission and photofragment absorption