Atomic interferometry in gravitational fields: Influence of gravitation onthe beam splitter

The laser induced splitting of atomic beams in the presence of a gravitatio nal field is analyzed. In the frame of a quasiclassical approximation, the motion of the atomic beam through a laser region with rectangular profile i s calculated. Beside the usual beam splitting due to the atom-laser interac tion, an additional splitting occurs due to the anomalous effective interac tion with the gravitational field. In a first order approximation in the gr avitational acceleration, the outcome of an atom interferometry experiment is given, which includes the various corrections owing to the gravitational modification of the beam splitting process.