We demonstrate an efficient scheme for continuous trap loading based upon spatially selective optical pumping. We discuss the case of
1S0 calcium atoms in an optical dipole trap (ODT), however, similar strategies should be applicable to a wide range of atomic species, which do not permit efficient conventional trap loading. Our starting point is a moderately cold $(\ensuremath{\approx}300\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K})$ and dense $(\ensuremath{\approx}9\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3})$ reservoir of metastable
3P2 atoms in a magneto-optic trap (triplet MOT). A focused
532nm laser beam produces a strongly elongated optical potential for
1S0 atoms with up to $350\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ well depth. A weak focused laser beam at
430nm, carefully superimposed upon the ODT beam, selectively pumps the
3P2 atoms inside the capture volume to the singlet state, where they are confined by the ODT. The triplet MOT perpetually refills the capture volume with
3P2 atoms, thus providing a continuous stream of cold atoms into the ODT at a rate of ${10}^{7}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. Limited by evaporation loss, in
200ms we typically load $5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms with $3.5\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ peak density and axial and radial temperatures of 300 and $85\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$, respectively. After terminating the loading we observe evaporation during
50ms, typically leaving us with
105 atoms with nearly equal radial and axial temperatures close to $40\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and a peak density of $5\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. A simple model is presented, which identifies the relevant physical mechanisms of the loading and decay dynamics. We point out that a comparable scheme could be employed to load a dipole trap with
3P0 atoms.
Metastable calcium atoms, produced in a magneto-optic trap (MOT) operating within the singlet system, are continuously loaded into a magnetic trap formed by the magnetic quadrupole field of the MOT. At MOT temperatures of 3 mK and 240 ms loading time, we observe $1.1\ifmmode\times\else\texttimes\fi{}{10}^{8}$ magnetically trapped
3P2 atoms at densities of $2.4\ifmmode\times\else\texttimes\fi{}{10}^{8}{\mathrm{cm}}^{\ensuremath{-}3}$ and temperatures of 0.61 mK. In a modified scheme, we first load a MOT for metastable atoms at a temperature of 0.18 mK and subsequently release these atoms into the magnetic trap. In this case, 240 ms of loading yields $2.4\ifmmode\times\else\texttimes\fi{}{10}^{8}$ trapped
3P2 atoms at a peak density of $8.7\ifmmode\times\else\texttimes\fi{}{10}^{10}{\mathrm{cm}}^{\ensuremath{-}3}$ and a temperature of 0.13 mK. The temperature decrease observed in the magnetic trap for both loading schemes can be explained only in part by trap size effects.
We report the construction and characterization of an experimental setup for producing a cold gas of
40Ca atoms and excite them to high Rydberg states with a resonant three-photon-excitation scheme. The apparatus comprises four stages, each designed in-house. An oven heated to
∼500∘C generates an atomic beam that is collimated by a capillary stack. The beam is sent into a passive, permanent-magnet-based Zeeman slower that reduces the atomic velocity to
30 m/s. The slow atoms are captured in a magneto-optical trap (MOT) and cooled to
1.0(3) mK with a trapping time of
16(2) ms. Ground-state atoms in the cold gas are excited to high Rydberg states via resonant excitation through the intermediate
4s4p1P1 and
4s4d1D2 states. The MOT is operated at the center of an electrode stack, which serves to apply continuous and pulsed electric fields and field-ionize the Rydberg atoms for detection. We benchmark our MOT against previous implementations and find its performance consistent with state-of-the-art results in terms of temperature and trapping lifetime. Finally, we demonstrate Rydberg spectroscopy of calcium, confirming the system's suitability for ultracold Rydberg physics experiments.
We describe a new system for laser cooling and trapping of neutral Calcium atoms employing the ¹S0 -¹ P1 resonant transition at 423 nm. An on-axis magneto-optical trap (MOT) is loaded from a Zeeman decelerated atomic beam. When a single laser is used, in order to avoid perturbation of the trap by the deceleration laser beam, this one has been tightly focused near the MOT center, with a waist size much smaller than the atomic cloud. In order to test the efficiency of this novel technique, we have then employed a second, independent decelerating laser, with a profile mode matched to the atomic beam. For an oven temperature of 580±C this system can load 1.2 (2) x 10(7) atoms in 16 (1) ms. By the spatial extension of the atomic cloud the one dimension rms velocity was estimated to be 136 (12) cm/s, corresponding to a temperature of 9 (2) mK. The variation of the number of trapped atoms as a function of laser detuning and intensity, trap magnetic field gradient and oven temperature is analyzed. Spatial structures of the trapped atoms, like stable rings created by vortex forces, have been observed. This is the first time that these structures, already observed in alkali-metal elements, are reported in MOTs of alkaline-earth elements.
Laser excitation of the
4s4p3P2−−4s3d1D2 transition in atomic calcium has been observed and the wavelength determined to 1530.5298(6) nm. The metastable
4s4p3P2 atoms were magnetically trapped in the quadrupole magnetic field of a magneto-optical trap. This state represents the only ``loss'' channel for the calcium atoms when laser cooled on the
4s21S0−−4s4p1P1 transition. A rate equation model shows that an order of magnitude more atoms are trapped in this state compared with those taking part in the main cooling cycle. Excitation of the
3P2 atoms back up to the
4s3d1D2 state provides a means of accessing these atoms. Efficient repumping is achieved if the 1530-nm laser is used in conjunction with a 672-nm laser driving the
4s3d1D2−−4s5p1P1 transition. In the present experiment, we detected about $4.5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ trapped
3P2 atoms, a relatively low atom density, and measured a lifetime of approximately 1 s, which is limited by background collisions.
Laser cooling and trapping in a magneto-optical trap (MOT) have been essential to the success of cold atom physics in the last decades. Recently, the application of the same techniques to molecules has begun. The complexity of even a simple diatomic molecule makes laser cooling difficult, but promises new applications in many areas of research. In this thesis I describe the development of the first three-dimensional MOT of calcium fluoride (CaF) molecules. First, a cryogenic buffer gas source was set up, producing a pulsed beam of 9.3*10^10 molecules per steradian per pulse with forward velocities around 170 m/s. A similar source for very large molecules was set up during a 5 month internship at the University of Vienna. Next, the molecular pulse was slowed down to the capture velocity of a MOT using chirped laser slowing, resulting in about 7*10^5 CaF molecules passing through the typical MOT volume of 1 cm^3 at velocities of 15+-5 m/s. A new deceleration method, called Zeeman-Sisyphus deceleration, was also investigated. In this method molecules move through a spatially varying magnetic field and are optically pumped between low- and high-field seeking states in such as a way that they are always losing kinetic energy. The method promises to deliver more slow molecules because the molecules are guided transversely as they are decelerated. A small prototype was built and the optical pumping step was tested successfully. Finally, 7.6*10^3 CaF molecules were trapped in a MOT and cooled to a temperature of 8.5 mK. The radial trap frequency is 2 pi*130 Hz and the damping constant is beta=9.5*10^2 s^-1. The lifetime is about 100 ms and depends strongly on the scattering rate. This MOT is an an ideal starting point for a wide range of new experiments with ultracold molecules.