Pulsed Optical-Optical Double Resonance Spectroscopy of ⁷Li₂

Abstract

One of the more fascinating applications of laser spectroscopy is the use of multiphoton phenomena to explore molecular electronic states which cannot be excited by one photon electric dipole transitions. Such studies are particularly rewarding when applied to diatomic molecular spectroscopy where a comparison between theory and experiment is often possible and of fundamental interest. The electronic state structure of Li₂, the least complex stable homonuclear diatomic besides molecular hydrogen, is an important example. Recently, we initiated OODR experiments on Li₂ with the intention of making a comprehensive spectroscopic investigation of the one-photon “forbidden” states [1–4]. A pulsed OODR technique was developed which is extremely useful for the characterization of states in this molecule that have been previously unobserved. The pulsed approach to OODR yields clean, simple spectra which are easily and unambiguously assigned. The enormous simplification of the OODR spectrum arises because (1) a single transition between the ground and intermediate state can be selectively pumped by one laser while a second laser is scanned to produce excitation from the populated intermediate level to the final states; and (2) the amount of relaxation within the intermediate state can be controlled by adjusting the delay time separating the pump laser pulse from the scanned laser pulse.