Bragg diffraction of an atomic wave packet in a retroreflective geometry with
two counterpropagating optical lattices exhibits a light shift induced phase.
We show that the temporal shape of the light pulse determines the behavior of
this phase shift: In contrast to Raman diffraction, Bragg diffraction with
Gaussian pulses leads to a significant suppression of the intrinsic phase shift
due to a scaling with the third power of the inverse Doppler frequency.
However, for box-shaped laser pulses, the corresponding shift is twice as large
as for Raman diffraction. Our results are based on approximate, but analytical
expressions as well as a numerical integration of the corresponding
Schr\"odinger equation.Comment: 6 pages, 5 figure
