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Based on Maxwell-type linearized Einstein Eqs of gravity, new ground-base torsion balance experiments are proposed to detect gravito-magnetic forces due to the rotation of the Earth. An optic system is employed to enlarge the effects so that the predicted effects are measurable by the proposed ground-based experiments.

The Lagrange points of the Sun/Earth pair form an interesting reference frame corotating with the Earth around the barycenter of the pair. Here we propose to use them as a base for a “rigid” physical loop allowing for the propagation of electromagnetic signals along a closed contour. If a gravito-magnetic field is concatenated with the loop, it produces an asymmetry of the times of flight in opposite directions, just as for the classical Sagnac effect. Due to the large scale of the loop, an experiment based on these premises could allow for a measurement of the angular momentum of the Sun and also the detection of the angular momentum of the dark halo of the Milky Way, if it exists.

We present here the proposal to use the LISA interferometer for detecting the gravitomagnetic field due to the rotation of the Milky Way, including the contribution given by the dark matter halo. The galactic signal would be superposed to the gravitomagnetic field of the Sun. The technique to be used is based on the asymmetric propagation of light along the closed contour of the space interferometer (Sagnac-like approach). Both principle and practical aspects of the proposed experiment are discussed. The strategy for disentangling the sought for signal from the kinematic terms due to proper rotation and orbital motion is based on the time modulation of the time of flight asymmetry. Such modulation will be originated by the annual oscillation of the plane of the interferometer with respect to the galactic plane. Also the effect of the gravitomagnetic field on the polarization of the electromagnetic signals is presented as an in principle detectable phenomenon.

In this talk the different possibilities offered by light (geometric effects, polarization effects, propagation delays and phase changes) for determining the local structure of space time, i.e., the gravitational field, in terms of the Riemann tensor, are discussed. Special attention is devoted to axially symmetric stationary gravitational fields. A description of the potentialities of ring lasers is presented, having direct reference to the GINGER project.

GINGER is a proposal for a new experiment aimed to the detection of the gravito-magnetic Lense-Thirring effect at the surface of the Earth. A three-dimensional set of ring lasers will be mounted on a rigid “monument”. In a ring laser a light beam traveling counterclockwise is superposed to another beam traveling in the opposite sense. The anisotropy in the propagation leads to standing waves with slightly different frequencies in the two directions; the resulting beat frequency is proportional to the absolute rotation rate in space, including the gravito-magnetic drag. The experiment is planned to be built in the Gran Sasso National Laboratories in Italy and is based on an international collaboration among four Italian groups, the Technische Universität München and the University of Canterbury in Christchurch (NZ).