Diffractive matter wave optics in time

We demonstrate a programmable sideband modulator for atoms. A controlled phase modulation is engraved on an atomic matter wave by interaction with a frequency-modulated light potential. The principle allows for tailoring atomic optical elements, e.g., temporal lenses, adjustable beam splitters, and holograms, in the time domain. As an illustration we present the time analog of a blazed grating that is generating asymmetric sidebands of atomic matter waves.