Recent theoretical work indicates that collisions between metastable alkaline-earth atoms (AEAs) in the presence of external magnetic fields should be largely determined by partial waves with large angular momenta even at very low temperatures. Unusually large inelastic collision cross sections were predicted and doubts have been raised regarding the feasibility of evaporative cooling of metastable AEAs in magnetic traps. Here we present experimental data for 40Ca[4s4p]3 P2 clearly confirming the asserted multichannel character of the collision mechanism. While elastic cross sections are found to be similar to the predicted values, inelastic cross sections exceed the calculations by an order of magnitude. Our results substantiate the expectation of inefficient evaporative cooling.

We demonstrate an efficient scheme for continuous trap loading based upon spatially selective optical pumping. We discuss the case of 1 S0 calcium atoms in an optical dipole trap (ODT), however, similar strategies should be applicable to a wide range of atomic species. Our starting point is a reservoir of moderately cold (≈ 300 µK) metastable 3 P2-atoms prepared by means of a magneto-optic trap (triplet-MOT). A focused 532 nm laser beam produces a strongly elongated optical potential for 1 S0-atoms with up to 350 µK well depth. A weak focused laser beam at 430 nm, carefully superimposed upon the ODT beam, selectively pumps the 3 P2-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 3 P2-atoms thus providing a continuous stream of cold atoms into the ODT at a rate of 10 7 s −1 . Limited by evaporation loss, in 200 ms we typically load 5 × 10 5 atoms with an initial radial temperature of 85 µK. After terminating the loading we observe evaporation during 50 ms leaving us with 10 5 atoms at radial temperatures close to 40 µK and a peak phase space density of 6.8 × 10 −5 . We point out that a comparable scheme could be employed to load a dipole trap with 3 P0-atoms.PACS numbers: 32.80. Pj, 82.20.Pm The unique spectroscopic features of two-electron systems and their usefulness for the fields of time metrology [1], cold collision physics [2, 3] and quantum gases [4] has led to extensive efforts to improve laser cooling and trapping techniques for alkaline earth (AE) atoms [5,6,7,8,9,10,11,12]. Calcium is a particularly interesting example, because, aside from its excellent performance in optical atomic clock scenarios [13,14], its singlet ground state (in contrast to the most abundant strontium isotope [15]) has a large positive scattering length with favorable prospects for reaching quantum degeneracy [16]. Optical trapping is a key technique in modern atomic physics, indispensible in numerous recent experiments with ultracold atoms and molecules [17]. In particular, if magnetic trapping techniques fail to work, as in the singlet manifold of the AE group, optical dipole traps (ODTs) practically have no alternative.ODTs typically provide good compression, but suffer from limited trap depths of several hundred µK, owing to limitations in available laser powers. Thus, efficient loading of ODTs typically requires a magneto-optic trap (MOT) permitting sufficiently low temperatures well below 100 µK, as available for alkaline atoms. Although magneto-optical trapping of AE-like atoms in the ground state is in fact possible using their principal fluorescence lines, the attainable temperatures of several mK are too high for efficient direct loading of an ODT. In some cases, e.g. for strontium or ytterbium, additional cooling by means of intercombination lines connecting to their ground states [5,10] have been used for ODT loading with large phase space densities. Unfortunately, this does not likewise apply to calcium, because o...

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 × 10 8 magnetically trapped 3 P2 atoms at densities of 2.4×10 8 cm −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 × 10 8 trapped 3 P2 atoms at a peak density of 8.7 × 10 10 cm −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.PACS numbers: 32.80. Pj, 42.50.Vk, 42.62.Fi, Earth alkaline atoms provide a unique combination of interesting spectroscopic features connected to their two valence electrons which give rise to singlet and triplet excitations. The singlet systems possess strong principle fluorescence lines well suited for laser cooling with remarkable efficiency. Yet, temperatures are limited to the mK domain, due to the absence of ground state Zeeman structure, a prerequisite for sub-Doppler techniques. The triplet systems, however, have readily accessible narrow band optical transitions that render possible refined laser cooling schemes with the promise of temperatures even beyond the microkelvin range. In fact, such schemes have recently been experimentally realized for strontium and calcium [1,2,3,4]. Owing to their spectroscopic peculiarities such ultracold earth alkaline samples open up new prospects for ultraprecise atomic clocks [5,6,7] and cold collision studies which allow direct comparisons with ab initio theoretical calculations [8,9,10]. The formation of Bose-Einstein condensates (BEC,[11]) for this exciting group of atoms appears particularly desirable.A key technique for obtaining BEC in alkalis and nobel gases has been magnetic trapping. This trapping technique outperforms optical techniques in two ways. It provides well controllable potential wells with sufficient steepness. The regime of high elastic collision rates, a precondition for efficient evaporative cooling, is thus easily accessible. Secondly, the presence of antibinding magnetic sublevels allows to actively force evaporation in a particular effective way by selectively expelling energetic atoms from the trap. The extension of this successful trapping technique to earth alkaline atoms may pave the route to BEC in this atom group. While the singlet ground state of these species lacks magnetic substructure, the ground state of the triplet system typically offers a particularly large Zeeman effect. Specifically, the long-lived 3 P 2 , m J =2 state appears appropriate for mag- * Electronic address: dhansen@physnet.uni-hamburg.de netic trapping and the formation of BEC. Recent calculations for calcium and strontium predict a positive scattering length (and thus stable BEC) for this state [...

A completely automated instrument for ice-fabric analysis has been built, tested and applied. The analysis of a thin section is performed in two steps. First, the section is loaded into the machine and is automatically imaged in about 16 min. Then, at a later time and convenient location, the grains in the section are identified from a stored image (either automatically or by the user), and the c-axis orientation of each grain is calculated at a rate of 1200 grains h^1. Comparison of automated results with manual Rigsby stage results shows excellent agreement. Diagnostics indicate that the accuracy of the new technique is 0.5³ in the c-axis orientation. Two specific applications are demonstrated: (1) the ability to measure internal grain orientations that may reveal internal stress, and (2) the ability to measure very thin thin sections. The latter, combined with the ability to zoom in on small regions of a section, will be useful for examining the fabric of fine-grained (51mm size grains) ice.

We report on Doppler-free frequency modulation spectroscopy and polarization spectroscopy in a discharge heat pipe of yet unexplored transitions connecting the metastable 3 P 2 ͑4s4p͒ state of calcium atoms with the multiply excited states 3 P 2 ͑4p4p͒ and 3 D 3 ͑4s3d͒. Calcium vapor is efficiently produced in a heat pipe operating in a small Pyrex cell filled with 2 torr of neon. A dc discharge running at 500 V efficiently populates the metastable triplet states. Narrow resonances with bandwidths of a few tens of MHz with excellent signal-tonoise ratios are observed, well suited as references for laser frequency stabilization. Examination of the Zeeman shifts lets us determine the Landé g factors of the excited states and compare them with the predictions based on the Russel-Saunders coupling scheme. We describe an economic, simple, and robust experimental setup that should work for other alkaline-earth-metal atoms like Mg and Sr, as well as for other solid elements with insufficient vapor pressures at room temperature.Alkaline-earth-metal atoms have attracted renewed interest recently because they offer a unique combination of features favorable for a wide range of applications including atomic interferometry ͓1,2͔, optical time standards ͓3͔, cold collision studies in reach of ab initio calculations ͓4-6͔, and studies of ultracold or quantum degenerate atomic gases outside the alkali-metal domain ͓7,8͔. Many interesting aspects of alkaline-earth-metal atoms are connected to the existence of long-lived metastable states accessible by laser sources in the visible and infrared. The desire to manipulate these states with the powerful techniques of laser cooling has motivated us to explore simple frequency referencing schemes, which provide narrow-band spectroscopic signals used to fix the laser frequency with regard to the atomic resonance of interest ͓9,10͔. In experiments with alkali-metal atoms in their ground states, frequency reference schemes are readily provided via Doppler-free spectroscopy in simple vapor cells owing to the high vapor pressure at room temperature ͓11͔. In contrast, alkaline-earth metals like calcium need to be heated significantly in order to obtain sufficient vapor pressure and the population of the metastable state requires operation of a discharge. A possible strategy is the use of a hollow cathode lamp. In such lamps, the discharge is derived from a hollow cathode made of the material of interest-for example, calcium; i.e., the discharge produces a calcium vapor by sputtering and at the same time populates the metastable state. In Ref. ͓12͔, Doppler-free signals with several tens of MHz linewidths have been obtained both with optogalvanic spectroscopy ͓13͔ and more directly by saturation spectroscopy. In both cases, by means of intermodulation techniques a signal-to-noise ratio of about 10 was achieved. Signal sizes in this approach are limited by the sputtering efficiency, while the use of intermodulation techniques based on mechanical choppers limits servolock applications to a band...