Laser spectroscopy of the 1001-nm ground-state transition in dysprosium

We present a direct excitation of the presumably ultranarrow $1001-\mathrm{nm}$ ground-state transition in atomic dysprosium. By using resonance ionization spectroscopy with pulsed Ti:sapphire lasers at a hot cavity laser ion source, we were able to measure the isotopic shifts in the $1001-\mathrm{nm}$ line between all seven stable isotopes. Furthermore, we determined the upper level energy from the atomic transition frequency of the ${}^{164}\mathrm{Dy}$ isotope as $9991.004\left(1\right){\mathrm{cm}}^{-1}$ and confirm the level energy listed in the NIST database. Since a sufficiently narrow natural linewidth is an essential prerequisite for high-precision spectroscopic investigations for fundamental questions, we furthermore determined a lower limit of $2.9\left(1\right)\mu \mathrm{s}$ for the lifetime of the excited state.

Figure 1

Sketch of the atomic beam mass spectrometer with ion flight path (yellow) and laser beams in anticollinear (solid red, solid blue) and perpendicular, crossed beam (dashed red) geometry. In the latter case, the first extraction electrode is put on a positive voltage to act as an ion repeller.

Figure 2

Indirect measurement of the upper energy level belonging to the $1001-\mathrm{nm}$ transition. (a) Measurement scheme consisting of a three-step resonant excitation, addressing an autoionizing state (AI) above the first ionization potential $\mathrm{IP}=47901.76{\mathrm{cm}}^{-1}$ of dysprosium [28], together with the additional dip step. (b) Ion counts as a function of the dip-step wave number.

Figure 3

Isotope shift measurement for the $1001\text{-nm}$ ground-state transition. (a) Excitation scheme. (b) Ion counts as a function of first excitation step frequency $\nu$ relative to the atomic transition frequency ${\nu }_{164}=299.5228\left(1\right)\mathrm{THz}$ of the ${}^{164}\mathrm{Dy}$ isotope.

Figure 4

Isotope shift measurement for the $741\text{-nm}$ ground-state transition. (a) Excitation scheme. (b) Ion counts as a function of first excitation step frequency $\nu$ relative to the atomic transition frequency ${\nu }_{164}=404.5990\left(1\right)\mathrm{THz}$ of the ${}^{164}\mathrm{Dy}$ isotope. Laser side modes are clearly visible.

Figure 5

Lifetime measurements in the 741- and 1001-nm transitions obtained by delaying the ionization laser pulse. For better readability, we added a random offset to the ion signal of the $741\text{-nm}$ transition.