We propose an underground experiment to detect the general relativistic effects due to the curvature of space-time around the Earth (de Sitter effect) and to the rotation of the planet (dragging of the inertial frames or Lense-Thirring effect). It is based on the comparison between the IERS value of the Earth rotation vector and corresponding measurements obtained by a triaxial laser detector of rotation. The proposed detector consists of six large ring lasers arranged along three orthogonal axes. In about two years of data taking, the 1% sensitivity required for the measurement of the Lense-Thirring drag can be reached with square rings of 6 m side, assuming a shot noise limited sensitivity (20 prad/s/root Hz). The multigyros system, composed of rings whose planes are perpendicular to one or the other of three orthogonal axes, can be built in several ways. Here, we consider cubic and octahedral structures. It is shown that the symmetries of the proposed configurations provide mathematical relations that can be used to ensure the long term stability of the apparatus

Laser-induced breakdown spectroscopy (LIBS) is a promising technique for in situ elemental analysis. A new mobile instrument for LIBS analysis, developed in a collaboration between Marwan Technology s.r.l. and the Applied Laser Spectroscopy Laboratory in Pisa, is presented, and some applications of it and results from it are outlined. The innovative experimental set-up, based on the use of two suitably retarded laser pulses and a standardless analysis procedure, which overcomes problems related to matrix effects, greatly improves the potential of this technique for accurate quantitative analysis.

Ring laser (RL) gyroscopes are, at present, the most precise sensors of absolute angular velocity. In the near future, their application is foreseen to provide ground based tests of General Relativity. We have recently proposed a tri-axial array of RLs that can reach the sensitivity, accuracy, and long term stability required to measure the inertial frame dragging induced by the rotating Earth, as predicted by General Relativity. The effect, also known Lense-Thirring effect, amounts for the Earth to 1 part in 10 9 of its rotation rate, thus requiring an unprecedented sensitivity and accuracy of experimental apparatus. An array of at least 3 RLs would allow us to measure not only the rotation rate, i.e. the angular velocity modulus, but also the angular velocity vector. In this way, having at disposal the time series of the daily estimate of Earth rotation vector from the International Earth Rotation and Reference System Service, it would be possible to isolate the Geodetic and Lense-Thirring contributions. Our proposal GINGER (Gyro-scopes IN GEneral Relativity) is intended to push the present knowledge of RL physics and technology to achieve an accuracy in the estimation of the Earth rotation rate of 1 part in 10 9. In the experimental apparatus we have to account for systematic errors resulting from non linear dynamics of the active laser medium, and changes of the optical cavity geometry. The redundancy of the array, e.g. the addition of a ring almost parallel to the Earth rotation axis, should allow for the reduction of such errors at the level of the geometry control. In this contribution we describe the intermediate prototypes GP2 and GEMS (GINGER External Metrology System) devoted to control the geometrical fluctuations of a RL cavity and the 3D geometry of the RL array (dihedral angles among RLs), respectively.

Abstract. GINGER (Gyroscopes IN General Relativity) is a proposal for an Earth-based experiment to measure the Lense-Thirring (LT) and de Sitter effects. GINGER is based on ring lasers, which are the most sensitive inertial sensors to measure the rotation rate of the Earth. We show that two ring lasers, one at maximum signal and the other horizontal, would be the simplest configuration able to retrieve the GR effects. Here, we discuss this configuration in detail showing that it would have the capability to test LT effect at 1%, provided the accuracy of the scale factor of the instrument at the level of 1 part in 10 12 is reached. In principle, one single ring laser could do the test, but the combination of the two ring lasers gives the necessary redundancy and the possibility to verify that the systematics of the lasers are sufficiently small. The discussion can be generalised to seismology and geodesy and it is possible to say that signals 10-12 orders of magnitude below the Earth rotation rate can be studied; the proposed array can be seen as the basic element of multi-axial systems, and the generalisation to three dimensions is feasible adding one or two devices and monitoring the relative angles between different ring lasers. This simple array can be used to measure with very high precision the amplitude of angular rotation rate (the length of the day, LOD), its short term variations, and the angle between the angular rotation vector and the horizontal ring laser. Finally this experiment could be useful to probe gravity at fundamental level giving indications on violations of Einstein Equivalence Principle and Lorenz Invariance and possible chiral effects in the gravitational field.