Optogalvanic spectroscopy of two-photon dissociation of Tl2 at 532 nm producing large population inversion between Tl(7 2S1/2) and (6 2P3/2) states

This paper reports the first time achievement of large population inversion between thallium 7 2S1/2 and 6 2P3/2 states through two-photon dissociation of pure Tl2 molecules. The second harmonic of a Nd–YAG laser at 532 nm is used to cause two-photon absorption in Tl2 from ground state Ou− to the repulsive state associated with the atomic 7 2S and 6 2P1/2 states. The relative population of the product atomic species is determined by using a tunable dye laser pumped by the third harmonic of a Nd–YAG laser. The dye laser beam focused for complete spatial and temporal overlap with the photodissociaiton pulse excites the product states to known atomic Rydberg states with subsequent ion detection. Prompt population inversion amounting to 100% is achieved. It is shown that photodissociation transition is mediated through predissociation of the upper bound state to a repulsive state correlated with Tl(7 S1/2) in the region of large internuclear separation.