Precise pulsed laser spectroscopy in the visible and far uv region: toward the measurement of the 11S-21S interval in atomic helium

Precise optical measurements have so far been conducted mainly in the visible and near-uv part of the spectrum. Extension to the far uv region depends on the development of tunable coherent sources that provide high resolution, accurate wavelength metrology, and a large photon flux. As part of our ongoing effort to measure the ionization energy of atomic helium by two- photon excitation at 120.28 nm, we have developed improved methods for generating vuv radiation in the vicinity of 120 nm, and for accurately measuring the systematic frequency shifts that occur during amplification and nonlinear mixing of nanosecond laser pulses.