Matter waves of cold rubidium atoms (from a magneto-optical trap) have been manipulated and imaged with optical tools of two kinds: an “absorptive” light mask and a phase grating.; The absorptive mask, also termed “optical mask”, is a standing wave of light in resonance with an open atomic transition. The mask depletes the initial ground state population everywhere except in a narrow range around the nodes. Pulses of the optical mask have been used to observe interference of atomic matter waves and to create gratings in the density of atoms (in a particular hyperfine internal state) with period as small as 1/10 of the optical wavelength. These density structures and the interference phenomenon (the so-called Talbot-Lau effect) have been monitored in real time using an original imaging technique also based on the optical mask. The instrumental width of the imaging technique is a small fraction of the optical wavelength.; The other optical tool for de Broglie waves, the phase grating, is a pulse of an off-resonant standing wave. Interaction of two or more such pulses with a cold thermal gas of atoms also produces modulation of density with sub-wavelength periodicity and allows to observe matter-wave interference effects.; The techniques for creating small size structures as well as for imaging them in real time may be of interest for nanofabrication applications.
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