Bragg spectroscopy in optical lattices

Ultracold atoms with optical lattices provide an ideal model system. This paper presents measurement of a momentum-resolved excitation spectrum in such a quantum model system of a crystal by means of Bragg spectroscopy. For the first time, first and second bands were measured with high resolution along a slice through the whole Brillouin zone. Measurements were performed at several lattice depths and, furthermore, the density and pulse area dependence of the excitation energy were systematically studied.