Fabio Stefani

Measuring Gravito-magnetic Effects by Multi Ring-Laser Gyroscope

SUMMARY We propose an under-ground experiment to detect the general relativistic effects due to the curvature of space-time around the Earth (de Sitter effect) and to 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 tri-axial 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

Two-way optical frequency comparisons at 5*10^-21 relative stability over 100-km telecommunication network fibers

m

DJOSER: Analytical Thermal Simulator for Multilayer Electronic Structures. Theory and Numerical Implementation

side, assuming a shot noise limited sensitivity (

Validation of the DJOSER analytical thermal simulator for electronic power devices and assembling structures

20 prad/s/\sqrt{Hz}

A laser gyroscope system to detect the gravito-magnetic effect on Earth

). The multi-gyros 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 octahedron structures. The symmetries of the proposed configurations provide mathematical relations that can be used to study the stability of the scale factors, the relative orientations or the ring-laser planes, very important to get rid of systematics in long-term measurements, which are required in order to determine the relativistic effects.

Laser gyroscopes for very high sensitive applications

By using two-way frequency transfer, we demonstrate ultra-high resolution comparison of optical frequencies over a telecommunication fiber link of 100 km operating simultaneously digital data transfer. We first propose and experiment a bi-directional scheme using a single fiber. We show that the relative stability at 1 s integration time is 7 10^18 and scales down to 5 10^21. The same level of performance is reached when an optical link is implemented with an active compensation of the fiber noise. We also implement a real-time two-way frequency comparison over a uni-directional telecommunication network using a pair of parallel fibers. The relative frequency stability is 10^15 at 1 s integration time and reaches 2 10^17 at 40 000 s. The fractional uncertainty of the frequency comparisons was evaluated for the best case to 2 10^20. These results open the way to accurate and high resolution frequency comparison of optical clocks over intercontinental fiber networks.

Cascaded optical link on a telecommunication fiber network for ultra-stable frequency dissemination

This paper presents a steady-state thermal simulation strategy called DJOSER, which is dedicated primarily but not exclusively to packaging structures for electronic devices. It is applicable to structures that can be likened to a set of homogeneous layers stacked one on top of the other and possibly separated by thermal contact resistances, where the dissipated powers are due to two-dimensional heat sources distributed on the interfaces between the layers. A broad range of contour conditions and types of dissipated powers is included to make the models as close as possible to the typical structures of modern assembly technologies. Flow and temperature distributions are obtained via a system of integral equations that can be translated directly, with the usual squaring techniques, into a linear algebraic system

High sensitivity rotation measurements with a mid-size laser gyroscope

The present communication deals with the tests for the validation of the DJOSER steady-state thermal simulation program, purposely designed for power electronic assembling structures and which is based on the resolution of analytical relationships. The validation experiments were carried out theoretically by comparing the thermal maps with those obtained using standard finite-elements programs and yielding temperature accuracy below 1%. Experimental tests were also performed on purposely built multi-layer structures and industrial circuits with power diodes mounted in naked-chip configuration. The simulated maps were compared with accurate thermo-graphic recordings and showed a good agreement, testifying the validity of the mathematical model.

GINGER - Toward an experimental test of General Relativity

Ring lasers are inertial sensors for angular velocity based on the Sagnac effect. In recent years they have reached a very high sensitivity and accuracy; the best performing one, the ring Laser G in Wettzell (Germany), a square ring with 16 m perimeter, has reached a sensitivity of 12prad/s very close to the shot noise limit inferred from ring-down time measurements. On this basis it is expected that an array of six square ring lasers of 36 m perimeter, can perform a 1% accuracy test for the measurement of the Lense-Thirring frame dragging after 2 years of integration time. Essential for this measurement is the comparison between the Earth angular velocity and orientation in space measured with the ring array and compared to the measurement series maintained by the International Earth Rotation and Reference System Service (IERS), which measures Earth Rotation and pole position with respect to remote quasars. It has been shown that the accuracy of G in Wettzell is limited by the low frequency motion of the near surface laboratory, which is of the order of several prad/s, roughly 100 times larger than the Lense-Thirring contribution. For this reason the entire experiment should be placed in a quite underground laboratory, where these perturbations are reduced. The feasibility to properly place such a device inside the GranSasso INFN National Laboratory has been investigated.

A heterodyne frequency-stabilization method for large ring laser gyroscopes with Sub-nW output power

We present a summary of the recent results obtained with the “G-Pisa” laser gyroscope prototype in the field of rotational metrology. The experimental apparatus consists in an He-Ne laser having a planar square cavity 1.35 m in side that can be operated both in the vertical and in the horizontal plane. For about one year, the ring laser has been utilized by the Virgo gravitational wave interferometer with the aim of estimating and monitoring the local rotational noise which is degrading the performances of its inertial suspensions. Results in the field of environmental monitoring for the improvement of the suspension control as well as the results in the field of rotational seismology are presented. In the last part of the paper we present some considerations about the possibility of performing a ground-based General Relativity test using an array of ring lasers.