The condition of energy conservation in a two-beam grating interference ele
ment imposes a phase shift of m pi on the diffraction order m of one of the
two incident beams relative to the same order of the other beam. The expre
ssions of the resulting interference products are given and their implicati
ons for a diffractive interferometric displacement sensor are discussed. (C
) 2001 Society of Photo-Optical Instrumentation Engineers.