A single Sr+ atom was confined in a radio-frequency quadrupole trap and laser cooled with resonant laser light. Examination of the transition Doppler profile indicated an ion kinetic temperature of less than 500 mK. Quantum jumps into and out of the metastable 4d(2)D(5/2) level were observed by laser excitation on the electric-quadrupole-allowed transition from the ground state at 674 nm. The dark and bright periods in the strong fluorescence showed variations owing to the applied driving field on the electric-quadrupole transition. These results provide an improved determination of tau = 372 +/- 25 msec for the natural metastable-state lifetime.
The first application, to our knowledge, of an all-solid-state system of lasers to the study of a single cooled trapped Sr(+) ion is described. Quantum jumps have been observed by driving the 674-nm 5s(2)S(1/2)-4d(2)D(5/2) transition, and preliminary observations of the line shape are reported. An upper limit for the temperature of a single ion, derived from the 674-nm linewidth, was 200 mK. If non-Doppler sources of broadening such as unresolved Zeeman structure dominate, then the temperature limit would be even lower.
The development of an all-solid-state systems of lasers is described for the cooling and probing of strontium ions in a radio-frequency (rf) trap. The Sr+ ions created within the rf trap are laser cooled by repeated cycling on the 422 nm 2S1/2 - 2P1/2 resonance transition. The 422 nm light was generated from a single mode 70 mW 844 nm diode laser, whose output was frequency doubled to 422 nm in a KNbO3 crystal inside a resonant enhancement cavity. Decays from the Sr+ upper resonance level into the 2D3/2 metastable state remove ions from the cooling cycle. This loss was prevented by driving the 1092 nm 2D3/2 - 2P1/2 transition using a Nd3+-doped fiber laser, diode-pumped at 826 nm. The 2S1/2 - 2D5/2 optical 'clock' transition at 674 nm has a natural linewidth of 0.4 Hz and may be probed with an AlGaInP laser diode. The laser diodes at 844 nm and 674 nm are both collimated using a piezo-mounted GRIN rod which also provides longitudinal mode selection. The spectral output is optically narrowed using resonant optical feedback.
An optical frequency standard, based on the 674 nm 2S1/2-2D5/2 'clock' transition in a laser cooled trapped strontium ion is currently being evaluated at the UK National Physical Laboratory. The probe laser is a narrowed AlGaInP diode laser locked to a highly-stable and ultra-low- expansion high-finesse cavity. Laser linewidths of less than 200 Hz have been observed, measured by scanning over a single Zeeman component at 674 nm. The development of this laser is described, together with factors currently limiting the observed linewidth. Three 88Sr+ traps are now in operation, and the probe laser source can be simultaneously locked to the center of the 2S1/2 - 2D5/2 Zeeman multiplet in any two of the three traps, allowing a comparison between them. Recent results on this comparison are presented.
We demonstrate laser cooling of single174Yb+ions stored in a rf trap. Single174Yb+ions were loaded using a natural isotope mixture as source. To locate a single ion at the center of the trap, and consequently, to minimize the micromotion caused by the rf driving field, we introduced two compensation electrodes and applied dc voltages to them and to one of the endcap electrodes. We estimated the temperature of a trapped single174Yb+ion to be 150 mK from the residual Doppler width of the spectra observed by a frequency sweep of the cooling laser. In the estimation, the saturation broadening in the spectra was substituted by measurement of the power dependence of the spectral width. To count the number of trapped174Yb+ions, we detected sudden drops in the fluorescence intensity (quantum jumps) of individual ions caused by pumping to and deexcitation of the2F7/2state. We found that deexcitation of the2F7/2state is possible by driving the2F7/2–1D[3/2]3/2transition at 760 nm and the2F7/2–3D[9/2]7/2transition at 828 nm, in addition to the former methods of driving the2F7/2–1D[5/2]5/2transition at 639 nm and the2F7/2–2D5/2transition at 3.43 µm.
We performed laser spectroscopy of
In+ ions stored in a radio-frequency trap. The 5
s2 1S0\ensuremath{\rightarrow}5s5p
3P1 transition at 230.6 nm was excited and its hyperfine splitting and isotope shift have been measured. The lifetime of the
3P1 state was measured using intensity modulated laser excitation: \ensuremath{\tau}
(3P1)=0.44(4) \ensuremath{\mu}s. A single indium ion was laser cooled using this intercombination line and dark periods in the fluorescence were observed when the metastable
3P0 state was populated by a magnetic dipole decay from
3P1. The radiative lifetime of the forbidden transition
3P0${\ensuremath{\rightarrow}}^{1}$
S0 was determined from the duration of the dark periods: \ensuremath{\tau}
(3P0)=0.14(2) s. This value is compared to calculations based on perturbation theory. Prospects for an optical frequency standard using the narrow 5
s2 1S0\ensuremath{\rightarrow}5s5p
3P0 resonance at 236.5 nm of a single laser-cooled indium ion are discussed.