Abstract

A new detection scheme has been developed to probe the continuum structure of H₂ and its isotopomers above the second dissociation limit, to H(1s) + H(2s or 2p), The excitation scheme is adopted from Refs, 1 and 2; two 193-nm photons generated by nonlinear mixing are absorbed by the ground state molecules to prepare the EF state, and a transformlimited pulsed ~677 nm probe laser subsequently excites the threshold region. To provide sensitive state-selective detection, the 2s or 2p product atoms are excited by a third laser at 366 nm to n = 40 high Rydberg states. The n = 40 Rydberg atoms are efficiently detected by delayed pulsed-field ionization. This scheme significantly reduces the power requirements for probe and detection lasers compared with earlier work.1-2 Therefore power broadening is nearly eliminated and sensitivity is improved. Since the 2s hydrogen atom is metastable, the detection laser can be delayed to detect 2s atoms alone or operated simultaneously with the 677-nm laser to detect both 2s and 2p atoms.

© 1997 Optical Society of America