Two different isotopes-(85)Rb and (87)Rb-have been captured simultaneously in one magneto-optical trap. The trap parameters could be chosen nearly independently for the two isotopes. The trap loss rates that are due to collisions between atoms of different isotopes have been measured in the low-intensity limit.

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Tw-dimensional traps for ultracold atomic gases are ofintercsl for the inwstigation of degenerate garcs, for waveguide experiments in atgm optics as w 1 1 for the redimtion of B cw atom laser [I].In order to load an optical surface trap, a cloud of metastable is5 argon atoms is released from a MOr and falls onto a gold-coated prism surface covered by evaneacent light fields that are generated by two laser beams through suiface~plasmon excitation (cf. Fig. la). W e use the first of these fields at 811 nm as an evanrrcmt-light mirror for the iiicoining Isi atoms. whereas the second ficld at 715 nm optically pumps the iltonri to the metastable lr, statc. ideally ai their classical turning point. We rcflcct the trapping laser beam at the \ ' I ( E I I U~ int.erfarruf tlir surface, thus creating 8 standing-mvc pattcm. This bparri ib blur drturied by 200 pm vith respect to the 1&p4 transition at 7% ~m , atid gmerstes a periodic 2D optical potential in which e fraction of the isp atonis i s stuird [2]. FIG. la FIG. l b In the expciimcnt.weturii off the pumping laser before turning off the trap and iriraring the stored Is3 atoms. With high temporal resolution; they can be detrrtpri tliruugli dectrons that UP ejected due to deexitation at the surface. Erprrimental results are shown in Fig. lb. The lower half of the figure shows the difTernirr of t w time-of-flight spcctra taken with and without the trapping beam. resperiiurlg. U'itliin our temporal resolution of loups: the atoms bit the surface instantaneourly after switching off this bcitm. giving rim to D single dara point. As shown in the upper half of the figure. alums are stored in the trap for several 10 ms. F a a red detuning of the reflection laser. DO trapping of atoms is observed. -We %re going to present a detaild study of the loading mechanism.

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