  Within the combined potential of an optical lattice and a harmonic magnetic
trap, it is possible to form matter wave packets by intensity modulation of the
lattice. An analysis of the production and motion of these wave packets
provides a detailed understanding of the dynamical evolution of the system. The
modulation technique also allows for a controllable transfer (de-excitation) of
atoms from such wave packets to a state bound by the lattice. Thus, it acts as
a beam splitter for matter waves that can selectively address different bands,
enabling the preparation of atoms in selected localized states. The combination
of wave packet creation and de-excitation closely resembles the well-known
method of pump-probe spectroscopy. Here, we use the de-excitation for precision
spectroscopy of the anharmonicity of the magnetic trap. Finally, we demonstrate
that lattice modulation can be used to excite matter wave packets to even
higher momenta, producing fast wave packets with potential applications in
precision measurements.
