On the diffraction correction in absolute gravimetry

The field distribution of a Gaussian light beam introduces additional space-dependent phase shifts compared with that of a flat wave front. An expression for these phase corrections is derived for the case of a two-beam interferometer. The contribution from these diffraction-induced shifts to the g -value determined in absolute gravimetry is calculated. It is found that in the case of a beam waist of a few millimetres or smaller and, particularly, for unbalanced interferometers, a careful consideration of this effect is crucial if high accuracy is desired.