Laser Spectroscopic Measurement of Helium Isotope Ratios
Abstract
A sensitive laser spectroscopic method has been applied to the quantitative determination of the isotope ratio of helium at the level of 3He/4He = 10^-7 - 10^-5. The resonant absorption of 1083 nm laser light by the metastable 3He atoms in a discharge cell was measured with the frequency modulation saturation spectroscopy technique while the abundance of 4He was measured by a direct absorption technique. The results on three different samples extracted from the atmosphere and commercial helium gas were in good agreement with values obtained with mass spectrometry. The achieved 3-sigma detection limit of 3He in helium is 4 x 10^-9. This demonstration required a 200 micro-L STP sample of He. The sensitivity can be further improved, and the required sample size reduced, by several orders of magnitude with the addition of cavity enhanced spectroscopy.
Keywords
Cite
@article{arxiv.physics/0311121,
title = {Laser Spectroscopic Measurement of Helium Isotope Ratios},
author = {L. -B. Wang and P. Mueller and R. J. Holt and Z. -T. Lu and T. P. O'Connor and Y. Sano and N. C. Sturchio},
journal= {arXiv preprint arXiv:physics/0311121},
year = {2015}
}