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An atom laser produces a coherent output of matter waves, often by extracting atoms from a Bose-Einstein condensate. Unlike an optical laser, its output consists of massive atoms and responds strongly to gravity and atomic interactions.

In the demonstrated radio-frequency output-coupling method, a pulse transfers part of a trapped condensate into an untrapped magnetic substate. The released atoms leave the trap while retaining coherence associated with the condensate. Varying the pulse controls the extracted fraction. The experiment makes the analogy with a laser concrete, while an output coupler alone does not imply that the reservoir is continuously replenished.^[ref]

Wolfgang Ketterle helped produce and investigate Bose-Einstein condensation in a dilute sodium gas. Cooling a trapped sample into the quantum-degenerate regime produced a population concentrated in a common low-energy state.

Expansion images distinguished the narrow condensed component from the broader thermal cloud. Subsequent experiments used coherence and collective motion to test how the macroscopic population behaves as a matter wave. His Nobel lecture connects the condensation apparatus with interference experiments and the atom laser.^[ref][ref]