Large-angle adjustable coherent atomic beam splitter by Bragg scattering

Using a 'monochromatic' (single-axial-velocity) and slow (250 m/s) beam of metastable helium atoms, we realize up to eighth-order Bragg scattering and obtain a splitting angle of 6 mrad at low laser power (3 mW). This corresponds to a truly macroscopic separation of 12 mm on the detector. For fifth-order scattering, we have observed several oscillations of the splitting ratio when varying the laser power ('Pendelloesung oscillations'). The large splitting angle, the adjustable splitting ratio, and the cleanness of the split beams, with 200-μm rms width each, make the beam splitter ideal for a large-enclosed-area atom interferometer