Scientific activities such as the LISA mission, neutron-beam interferometry, and the determination of the silicon lattice parameter require the realisation of the meter by laser interferometers with picometre accuracy and sensitivity and powered by stabilized laser sources. Therefore, the laboratory developed stabilized laser sources (@ 532nm and @ 633nm) and interferometric systems capable of measuring macroscopic displacements (several cm) with absolute errors of a few picometers. At the same time, it first developed "differential wavefront sensing" techniques capable of monitoring parasitic rotations with sub-nrad sensitivity. Finally, it has the theoretical, modelling and numerical skills necessary to evaluate the effects of diffraction and geometric phase in interferometric measurements.