Stochastic rainbow caustic observed with cold atoms - art. no. 065403

We report the direct observation of a type of rainbow caustic, In contrast to known examples, this caustic originates from a dissipative, stochastic p rocess. We have observed this when using cold Rb-87 atoms bouncing inelasti cally on an evanescent-wave atom mirror. The caustic appears as a sharp pea k at the lower edge of an asymmetric velocity distribution of the bouncing atoms. The stochastic process is a spontaneous Raman transition due to phot on scattering during the bounce. The results are in good agreement with a c lassical calculation.