Transient atom optics: Reflection and transmission of atoms by a time-dependent laser field

Although there are many kinds of different techniques developed to manipulate atomic matter waves, a laser beam is still considered as the most effective ''optical element'' to manipulate atomic waves in atom optics. In the laser-based atom optic devices, the spatial profiles of a laser beam play a central role in controlling the motion of atoms. By choosing different spatial profiles of laser beams, one can construct atom optic devices for different purposes. Recently experimental demonstrations of manipulation of centre of mass motion of atoms by time-dependent light field were reported.(18-19) In this paper we theoretically study the transient effects in atom optics by using a laser pulse train. The reflection and transmission of atoms through the laser pulse train are studied in detail. We find that the laser pulse train acts as both a spatial beam splitter and a ''temporal grating'' which can both reflect or transmit atoms in spatial domain and ''diffract'' atoms in the time domain.