We have produced a magneto-optical trap that simultaneously confines two different atomic species: sodium and potassium. A measurement of the sodium trap loss rate constant due to collisions with cold potassium atoms was performed. We extract this rate constant by measuring the temporal behavior of the loading process of the sodium trap in the presence and absence of cold potassium. The constant that is obtained can be qualitatively explained using simple existing models. Future applications of simultaneous trapping are discussed. PACS number(s): 32.80.Pj, 33.80.b, 34.50.s Very early in the development of optical traps, it was recognized that several novel collisional effects would be very important and would contribute to a better understanding of the atom-atom interactions. Contrary to the usual atomic collisions, at low temperatures the interaction times are very long and comparable to spontaneous emission times.Collisions become very sensitive to the long-range interatomic potentials and can be highly quantum mechanical in nature. Even more important is the role absorption and emission of radiation play: the probability of absorbing or emitting a photon during the collision time is no longer negligible. Therefore, the dynamics of the collisional process depends greatly on the internal states of the colliding atoms (11.The samples of cold atoms are usually provided by a magneto-optical trap (MOT) [2], in which several recently reported effects have been observed [3 -8]. All these experiments, and most of the theories developed to date, have in common the fact that they deal with a single atomic species. The first experimental "variation on this theme" has been performed by W. Siiptitz et al. [9].They have simultaneously cooled and trapped two different rubidium isotopes and measured a cross-isotope collisional rate. An even stronger variation would consist of studying cold collisions involving different atomic species. That could open up new and exciting possibilities. For example, sympathetic cooling [10 -12] of neutral atoms, where one species is cooled by interaction with a second one, should be possible. High resolution studies of molecular bond formation involving different alkalimetal atoms are also of fundamental interest.In this paper we present an experiment on the simultaneous magneto-optical trapping of two different atomic species, and report on the observation of cold collision effects involving different alkali-metal atoms. We confine simultaneously (in space and time) cold atoms of sodium and potassium and investigate the rate constant for collisional trap loss due to a process involving different species. The process is interpreted as a two-body collision and measured through the transient loading of the trap.Our magneto-optical trap operates in a room temperature glass vapor cell that contains separate sodium and potassium Permanent address: National Institute of Standards and Technology, PHYS A167, Gaithersburg, MD 20899.reservoirs. The initial vacuum in the cell is made by using a turbo mole...

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We have measured the total collisional loss rate for ultracold sodium atoms held in a magneto-optical trap operating on the D1 line. The collisional rate is extracted from the decay of the fluorescence from trapped atoms. We observe an intensity dependence corresponding to radiative escape and hyperfine changing collisions in the trap. The results obtained are compared with previous measurements for traps operating on the D2 line.