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.