Measurement of the $(3s3p){}^{1}P$–$(3s3d){}^{1}D$ isotope shift in Mg i

We present measurements of the isotope shift for the $(3s3p){}^{1}P-(3s3d){}^{1}D$ transitions at $881$ nm in Mg i. The three stable magnesium isotopes yielded a shift ${}^{24}\mathrm{Mg}$–${}^{25}\mathrm{Mg}$ of $(1342\pm 20)$ MHz and ${}^{25}\mathrm{Mg}$–${}^{26}\mathrm{Mg}$ of $(1175\pm 23)$ MHz. Measured shifts are consistent with recent relativistic many-body calculations of the mass effect.

Figure 1

Energy levels relevant for the ${}^{1}S\to {}^{1}P\to {}^{1}D$ spectroscopy. The linewidth of the ${}^{1}P$ level is 79 MHz; for the ${}^{1}D$ level it is 2 MHz.

Figure 2

Schematic experimental setup. A frequency generator ramps the $881$-nm laser piezo cryatal at $20$ mHz. The laser passes through an AOM, which is turned on and off by a square pulse at $60$ kHz. The first-order signal from the AOM is led into the reference cavity and the MOT. The spectroscopic signal is selected through an interference filter at $881$ nm and detected in a photomultiplier. Both the lock-in and the cavity signal is recorded.

Figure 3

Spectroscopic signal from the three Mg i isotopes—${}^{24}\mathrm{Mg}$,${}^{25}\mathrm{Mg}$,${}^{26}\mathrm{Mg}$—at $881$ nm. The top curve is cavity resonance lines, with the double peaks being the zeroth- and first-order diffraction from an AOM operating at $82.5$ MHz, repeated for each FSR.

Figure 4

Isotope shift for different values of current in the Helmholtz coils. The circles closer to the bottom of the figure belong to the ${}^{24}\mathrm{Mg}$–${}^{25}\mathrm{Mg}$ transition; the crosses closer to the top belong to the ${}^{25}\mathrm{Mg}$–${}^{26}\mathrm{Mg}$ transition. The error bars give a possible sensitivity to varying $B$ field at $\pm 0.4$ MHz per ampere for the ${}^{24}\mathrm{Mg}$–${}^{25}\mathrm{Mg}$ transition and $\pm 0.3$ MHz per ampere for the ${}^{25}\mathrm{Mg}$–${}^{26}\mathrm{Mg}$ transition.

Figure 5

${}^1{P}_1\to {}^1{D}_2$ fluorescence spectrum for ${}^{24}\mathrm{Mg}$ in constant magnetic field, with fit to five Voigt distributions plotted separately and together.