Atom interference in pulsed standing wave fields

We have studied sub-optical wavelength atomic gratings generated by the interference of atomic de Broglie waves in a time-domain interferometer. Three short optical standing-wave pulses, detuned from resonance with a cloud of approx. 100 μK ⁸⁵Rb atoms, act as phase gratings for atomic matter waves. The first two standing-wave pulses, separated by time T, produce a sequence of atomic density gratings of periods λ/2N, where λ is the optical wavelength and the integer N is the order of the grating. These gratings can be detected indirectly by the action of the third standing-wave pulse, which converts them into the first order gratings (with period λ/2). The resulting first order gratings, which appear at later times and carry information about the prior high order gratings, can be detected through the scattering of a traveling-wave light field. Using the sequence of three standing-wave pulses, we have experimentally demonstrated the formation of a grating with period λ/4 at time 1.5T after the first pulse. The dependence of our signals on the time separation of the pulses is in good agreement with our theoretical predictions. As far as we know, this is the first time when the formation of a high order matter-wave diffraction grating was observed in real time. This demonstrated ability to produce sub-wavelength structures makes our techniques applicable to atomic beam lithography.