Abstract

As part of our ongoing effort to measure the ionization energy of helium, we have developed a scheme to generate VUV radiation in the vicinity of 120 nm by resonant four-wave mixing in molecular hydrogen. We use two single-mode pulsed dye lasers, one at a fixed 606 nm wavelength and the other tunable in the visible red region. The first laser is tuned to two photon resonance with the ν=0, N=0 level of the EF state. The required 202 nm wavelength is generated by frequency tripling of 606 nm light, by using frequency doubling in KDP and sum- frequency mixing in β-BaB₂O₄. The second laser is tuned to produce tunable coherent difference-frequency radiation in the vicinity of 120 nm. This scheme is similar to that developed by Strauss and Funk¹ but has the advantage of using two red-dye lasers, greatly simplifying the metrology needed for high resolution VUV spectroscopy. We will report progress on a preliminary measurement of the 1s-2s interval in helium using two-photon excitation at 120.28 nm.

© 1992 Optical Society of America