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We have achieved Bose-Einstein condensation of 40 Ca, the first for an alkaline earth element. The influence of elastic and inelastic collisions associated with the large ground-state s-wave scattering length of 40 Ca was measured. From these findings, an optimized loading and cooling scheme was developed that allowed us to condense about 2·10 4 atoms after laser cooling in a two-stage magnetooptical trap and subsequent forced evaporation in a crossed dipole trap within less than 3 s. The condensation of an alkaline earth element opens novel opportunities for precision measurements on the narrow intercombination lines as well as investigations of molecular states at the 1 S-3 P asymptotes.PACS numbers: 03.75.Hh, 67.85.HjThe first Bose-Einstein condensate (BEC) of a dilute quantum gas in 1995 has opened completely new avenues in physics. In subsequent years this quantum degenerate state could be reached with different species (for a recent list of references see, e. g., [1]). By far most research has been performed on alkali atomic and molecular BECs apart from hydrogen, metastable helium, chromium, and ytterbium. So far, no member of the alkaline earth elements could be brought to quantum degeneracy despite considerable effort [2,3]. The alkaline earth elements have unique properties, e. g., their narrow intercombination transitions or their ground state without a magnetic moment. Due to the non-degenerate ground state in 40 Ca and in the other alkaline earth elements, the associated simpler molecule structure allows for more accurate investigations of collisions [4,5]. Moreover, the vanishing magnetic moment in the ground and excited state will allow for novel applications in atom interferometry not hampered by phase shifts due to magnetic fields. Calcium has a particularly large ground state scattering length that not only made it interesting but also difficult to realize a BEC.Calcium (like the other alkaline earth elements) shares these properties with ytterbium which has a similar electronic structure [6] but has a five hundred-fold larger line width of the 1 S 0 -3 P 1 intercombination transition. This 370 Hz line width at 657 nm made calcium for some time the optical frequency standard with the lowest uncertainty in the visible [7]. Both technologies, optical frequency metrology and the generation of a BEC, can now be combined for novel applications.In this letter we report on the preparation of a 40 Ca BEC. Starting point for our experiment is a magnetooptical trap (MOT) on the 1 S 0 -1 P 1 transition in the singlet system. The vanishing ground-state magnetic moment prevents sub-Doppler cooling of 40 Ca in a MOT. To cool the atoms further we use a second MOT stage on the narrow intercombination line 1 S 0 -3 P 1 allowing for temperatures in the MOT as low as 15 µK. For efficient cooling we increase the scattering rate of this transition by quenching the upper state [8]. During both MOT stages an optical dipole trap is overlapped with the MOT. In order not to interfere with the narrow line cooling we choo...

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Abstract. During the ACRIDICON-CHUVA field project (September–October 2014; based in Manaus, Brazil) aircraft-based in situ measurements of aerosol chemical composition were conducted in the tropical troposphere over the Amazon using the High Altitude and Long Range Research Aircraft (HALO), covering altitudes from the boundary layer (BL) height up to 14.4 km. The submicron non-refractory aerosol was characterized by flash-vaporization/electron impact-ionization aerosol particle mass spectrometry. The results show that significant secondary organic aerosol (SOA) formation by isoprene oxidation products occurs in the upper troposphere (UT), leading to increased organic aerosol mass concentrations above 10 km altitude. The median organic mass concentrations in the UT above 10 km range between 1.0 and 2.5 µg m−3 (referring to standard temperature and pressure; STP) with interquartile ranges of 0.6 to 3.2 µg m−3 (STP), representing 78 % of the total submicron non-refractory aerosol particle mass. The presence of isoprene-epoxydiol-derived secondary organic aerosol (IEPOX-SOA) was confirmed by marker peaks in the mass spectra. We estimate the contribution of IEPOX-SOA to the total organic aerosol in the UT to be about 20 %. After isoprene emission from vegetation, oxidation processes occur at low altitudes and/or during transport to higher altitudes, which may lead to the formation of IEPOX (one oxidation product of isoprene). Reactive uptake or condensation of IEPOX on preexisting particles leads to IEPOX-SOA formation and subsequently increasing organic mass in the UT. This organic mass increase was accompanied by an increase in the nitrate mass concentrations, most likely due to NOx production by lightning. Analysis of the ion ratio of NO+ to NO2+ indicated that nitrate in the UT exists mainly in the form of organic nitrate. IEPOX-SOA and organic nitrates are coincident with each other, indicating that IEPOX-SOA forms in the UT either on acidic nitrate particles forming organic nitrates derived from IEPOX or on already neutralized organic nitrate aerosol particles.