  We report on the observation of interference of a series of atom lasers. A
comb-like array of coherent atomic beams is generated by outcoupling atoms from
distinct Bose-Einstein condensates confined in the independent sites of a
mesoscopic optical lattice. The observed interference signal arises from the
spatial beating of the overlapped atom laser beams, which is sampled over a
vertical region corresponding to 2 ms of free fall time. The average relative
de Broglie frequency of the atom lasers was measured.
