Field shift analysis of visible and near-infrared argon transitions

We report a systematic study of the isotope shift of an argon atom for s-p and p-d transitions in the visible and the near-infrared regions. The isotope shifts were determined by saturation spectroscopy, and the measurements were effected by use of a standard error of approximately 1 MHz. Combining our spectroscopic measurements with the nuclear charge radii available from muonic transitions, we were able to extract the specific mass and the volume contributions to the isotope shift. In all the investigated transitions we observed a field shift contribution that is surprising for a light element like argon. Moreover, for p-d transitions we also found a field shift larger than for s-p ones, in spite of the fact that s orbitals experience more of the electron density at the nucleus. (C) 1999 Optical Society of America [S0740-3224(99)01505-2].