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 1s2s 1S0 states of 3He and 4He; the 1s2s 1S0 level of 3He is 7.8 ± 0.5 cm−1 below that of 4He.
© 1978 Optical Society of America
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