  Atom lasers based on rf-outcoupling from a trapped Bose-Einstein condensate
can be described by a set of generalized, coupled Gross-Pitaevskii equations
(GPE).
  If not only one but two radio frequencies are used for outcoupling, the atoms
emerging from the trap have two different energies and the total wavefunction
of the untrapped spin-state is a coherent superposition which leads to a pulsed
atomic beam.
  We present results for such a situation obtained from a 1D-GPE model for
magnetically trapped Rb-87 in the F=1 state. The wavefunction of the atomic
beam can be approximated by a sum of two Airy functions. In the limit of weak
coupling we calculate the intensity analytically.
