Interferometer for the IMGC rise-and-fall absolute gravimeter

Absolute gravity measurements are performed by absolute gravimeters that
sometimes show significant differences between their averaged values, e.g.
in occasion of international comparisons organized periodically by the
BIPM. Many sources of errors have been taken in consideration to evaluate
each uncertainty budget, nether the less in some cases the observed
differences from a general averaged value are statistically larger than
expected on the base of these evaluations; the main reason is that some
causes of uncertainty cannot be well quantified as are based only on
theoretical hypothesis.
On our side after investigating some sources of error regarding our
optical interferometer we here propose: 1) an optical design that
minimizes errors due to relative movements between the interferometer
parts; 2) a simple apparatus to be easily used to equilibrate the moving
corner-cube prism which constitutes the moving mirror of the
interferometer. With this two modifications implemented in the IMGC
absolute gravimeter, we believe to have reduced the uncertainty due to the
interferometer of about ten times.