Observing negligible collision trap losses: The case of alkaline-earth metals

We show that when cold collisions account for just a few percent of the total loss in magneto-optical traps, as for alkaline-earth metals, their contribution can be obtained by comparing the load and decay quasiexponential curves. We exemplify it by measuring the collision rate coefficient beta for calcium atoms at small trap laser detuning, which confirms the role of the long-lived (1)Pi(g) state at small internuclear separation. Systematic and simpler measurements of beta for alkaline-earth metals are important for cold collision theory, since these elements have nondegenerate ground state and no hyperfine structure. Our method has general applicability and should considerably reduce the experimental challenges associated with these important measurements.