Calcium and strontium atomic beams are cooled and trapped by using the 1S0-1P1 transition in the 400 nm region. The trapping of 8 isotopes, 40Ca, 42Ca, 43Ca, 44Ca, 84Sr, 86Sr, 87Sr and 88Sr, is observed. The decay rate of the trapped atom is found to be of the order of 10 ms and the average atomic velocity less than 1 m/s.
We report on a system for atomic beam deceleration and magneto-optical trapping of calcium atoms that uses the 1S0–1P1 transition, in which a single laser is used to trap and slow the atoms. The slower laser beam is focused near the magneto-optical trap’s center, which has a waist size much smaller than the atomic cloud such that its influence on the trapped atoms is greatly reduced. We also investigate the theoretical possibility of cooling by use of a two-photon (4s2)1S0–(4s5s)1S0 transition. Excitation near resonance with the 1P1 level results in an equilibrium temperature seven times smaller than the Doppler limit of the 1S0–1P1 transition.
We present a detailed investigation of strontium magneto-optical trap (MOT) dynamics. Relevant physical quantities in the trap, such as temperature, atom number and density, and loss channels and lifetime, are explored with respect to various trap parameters. By studying the oscillatory response of a two-level 1S0–1P1 88Sr MOT, we firmly establish the laser cooling dynamics predicted by Doppler theory. Measurements of the MOT temperature, however, deviate severely from Doppler theory predictions, implying significant additional heating mechanisms. To explore the feasibility of attaining quantum degenerate alkaline-earth samples via evaporative cooling, we also present the first experimental demonstration of magnetically trapped metastable 88Sr. Furthermore, motivated by the goal of establishing the fermionic isotope 87Sr as one of the highest-quality, neutral-atom-based optical frequency standards, we present a preliminary study of sub-Doppler cooling in a 87Sr MOT. A dual-isotope (87Sr and 88Sr) MOT is also demonstrated.
The efficiency of laser cooling in a thermal beam of calcium has been investigated under different cooling schemes. Special attention has been paid to analysis of the loss factor represented by the decay of atoms excited by the cooling laser to the 1P1 state into the metastable 1D2 level. The cooling scheme at a fixed laser frequency makes possible a good estimation of the branching ratio R between the decay probability from the 1P1 level to the ground 1S0 state and to the metastable 1D2 state. The measured value of (1.0 ± 0.15) × 105 seems high enough to produce only a small reduction in the cooling efficiency.
We present studies of resonance-enhanced photoionization for isotope-selective loading of Ca+ into a Paul trap. The ${4s}^{2}{}^{1}{S}_{0}\ensuremath{\leftrightarrow}4s4p{}^{1}{P}_{1}$ transition of neutral calcium is driven by a 423 nm laser and the atoms are photoionized by a second laser at 389 nm. Isotope selectivity is achieved by using crossed atomic and laser beams to reduce the Doppler width significantly below the isotope shifts in the 423 nm transition. The loading rate of ions into the trap is studied under a range of experimental parameters for the abundant isotope 40Ca+. Using the fluorescence of the atomic beam at 423 nm as a measure of the Ca number density, we estimate a lower limit for the absolute photoionization cross section of 170(60) Mb. We achieve loading and laser cooling of all the naturally occurring isotopes, without the need for enriched sources. Laser heating/cooling is observed to enhance the isotope selectivity. In the case of the rare species 43Ca+ and 46Ca+, which have not previously been laser cooled, the loading is not fully isotope selective, but we show that pure crystals of 43Ca+ may nevertheless be obtained. We find that for loading 40Ca+ the 389 nm laser may be replaced by an incoherent source.