Optical hyperfine structure in ${\mathrm{Ne}}^{21}$ has been observed using laser-induced line-narrowing techniques. The output from a long stabilized single-mode 1.15-μ He-Ne laser is focused into an external sample cell containing ${\mathrm{Ne}}^{21}$. The laser field resonates with the ${\mathrm{Ne}}^{21}$ 1.15-μ transition causing changes in the level populations over a narrow velocity range. Viewed along the laser axis, these population changes appear as narrow "change signals" superposed on the Doppler background of the spontaneous emission of the coupled 6096-Å transition. Analysis of the spectrum of these change signals, emitted parallel and antiparallel to the laser-field propagation direction, gives values for the hyperfine $A$ constants for the three levels involved. These constants are analyzed by means of theoretical expressions wherein $〈\frac{1}{r^3}〉$ of the $2p$ hole is the single important parameter. Combining the resulting value of ${〈\frac{1}{r^3}〉}_{2p\mathrm{hole}}$ for the $1s_4$ level with a previous measurement of $B\left(1\mathrm{}{s}_5\right)$ gives a value of $Q\left(1s\right)=(0.093\mathrm{}\pm 0.002)$ b, in agreement with an earlier less-accurate value. In addition, the ${\mathrm{Ne}}^{20,21,22}$ isotope shifts are measured at 1.15 μ and 6096 Å.

• Received 17 May 1971

DOI:https://doi.org/10.1103/PhysRevA.5.1036