Laser spectroscopy and cooling of Yb${}^{+}$ ions on a deep-UV transition

We perform laser spectroscopy of Yb${}^{+}$ ions on the 4$f^{14}6s{}^2{S}_{1/2}$-$4f^{13}5d6s$ ${}^{3}D{[3/2]}_{1/2}$ transition at 297 nm. The frequency measurements for ${}^{170}$Yb${}^{+}$, ${}^{172}$Yb${}^{+}$, ${}^{174}$Yb${}^{+}$, and ${}^{176}$Yb${}^{+}$ reveal the specific mass shift as well as the field shifts. In addition, we demonstrate laser cooling of Yb${}^{+}$ ions using this transition and show that light at 297 nm can be used as the second step in the photoionization of neutral Yb atoms.

Figure 1

Relevant energy levels and transitions of Yb${}^{+}$ (branching ratios given in percentages). ${\Gamma }_{D[3/2]}$, ${\Gamma }_D$, and branching ratio out of the ${}^2{P}_{1/2}$ state are taken from Ref. [9], ${\Gamma }_{D[3/2]}$ from Ref. [10], and the ${}^{3}D{[3/2]}_{1/2}$ branching ratio from Ref. [11].

Figure 2

Laser system to generate 297-nm light. Abbreviations: BBO: Beta barium borate crystal, EOM: electro-optic modulator, FP: fast piezotransducer, LP: low pass, Mod: laser current modulation, PBS: polarizing beam splitter, PD: photodiode, PID: feedback controller, SFG: sum frequency generation, SP: slow piezotransducer, TA: tapered amplifier.

Figure 3

Double-resonance spectrum of the ${}^2{S}_{1/2}$-${}^{3}D{[3/2]}_{1/2}$ transition in ${}^{176}$Yb${}^{+}$. Yellow (grey) line: Gauss fit. Transition frequencies have been determined by averaging ten spectra.

Figure 4

King plot of our data vs the data of Clark et al. [20]. The slope of the linear fit is used to determine the field shift.

Figure 5

Recorded 369-nm fluorescence while loading a single Yb${}^{+}$ with 297-nm light. Inset: Zoom into the onset of the fluorescence (each curve is the average of ten loadings). Yellow (light grey) curve: large detuning, ${\Delta }_{297\mathrm{nm}}=-400$ MHz. Blue (dark grey) line: expected fluorescence of a 100 K hot ion [22]. Black curve: sweep of ${\Delta }_{297\mathrm{nm}}$ from $-$200 to $-$60 MHz in 3 s after heating the oven leads to a high initial level of 369-nm fluorescence indicating a cold ion. In both cases ${\Delta }_{369\mathrm{nm}}=-{\Gamma }_P/2$.