Measurement of the He 1s2s^1S_0 isotopic shift using a tunable VUV anti-Stokes light source

Abstract

We describe a high-resolution, vacuum-ultraviolet spectroscopic technique based on a tunable, narrow-band, VUV, spontaneous anti-Stokes light source. The technique was used to measure the absolute energies of the 1s2s1S0 states of 3He and 4He; the 1s2s1S0 level of 3He is 7.8 ± 0.5 cm−1 below that of 4He.