1,654 research outputs found
A 1.82 m^2 ring laser gyroscope for nano-rotational motion sensing
We present a fully active-controlled He-Ne ring laser gyroscope, operating in
square cavity 1.35 m in side. The apparatus is designed to provide a very low
mechanical and thermal drift of the ring cavity geometry and is conceived to be
operative in two different orientations of the laser plane, in order to detect
rotations around the vertical or the horizontal direction. Since June 2010 the
system is active inside the Virgo interferometer central area with the aim of
performing high sensitivity measurements of environmental rotational noise. So
far, continuous not attempted operation of the gyroscope has been longer than
30 days. The main characteristics of the laser, the active remote-controlled
stabilization systems and the data acquisition techniques are presented. An
off-line data processing, supported by a simple model of the sensor, is shown
to improve the effective long term stability. A rotational sensitivity at the
level of ten nanoradiants per squareroot of Hz below 1 Hz, very close to the
required specification for the improvement of the Virgo suspension control
system, is demonstrated for the configuration where the laser plane is
horizontal
First deep underground observation of rotational signals from an earthquake at teleseismic distance using a large ring laser gyroscope
Recent advances in large ring laser gyroscopes (RLG) technologies opened the
possibility to observe rotations of the ground with sensitivities up to
over the frequency band of seismological interest
(0.01-1Hz), thus opening the way to a new geophysical discipline, i.e.
rotational seismology. A measure of rotations in seismology is of fundamental
interest for (a) the determination of all the six degrees of freedom that
characterize a rigid body motion, and (b) the quantitative estimate of the
rotational motions contaminating ground translation measurements obtained from
standard seismometers. Within this framework, this paper presents and describes
GINGERino, a new large observatory-class RLG located in Gran Sasso underground
laboratory (LNGS), one national laboratories of the INFN (Istituto Nazionale di
Fisica Nucleare). We also report unprecedented observations and analyses of the
roto-translational signals from a tele-seismic event observed in such a deep
underground environment
Analysis of ring laser gyroscopes including laser dynamics
Inertial sensors stimulate very large interest, not only for their
application but also for fundamental physics tests. Ring laser gyros, which
measure angular rotation rate, are certainly among the most sensitive inertial
sensors, with excellent dynamic range and bandwidth. Large area ring laser
gyros are routinely able to measure fractions of prad/s, with high duty cycle
and bandwidth, providing fast, direct and local measurement of relevant
geodetic and geophysical signals. Improvements of a factor would open
the windows for general relativity tests, as the GINGER project, an Earth based
experiment aiming at the Lense-Thirring test at level. However, it is
well known that the dynamics of the laser induces non-linearities, and those
effects are more evident in small scale instruments. Sensitivity and accuracy
improvements are always worthwhile, and in general there is demand for high
sensitivity environmental study and development of inertial platforms, where
small scale transportable instruments should be used. We discuss a novel
technique to analyse the data, aiming at studying and removing those
non-linearity. The analysis is applied to the two ring laser prototypes GP2 and
GINGERINO, and angular rotation rate evaluated with the new and standard
methods are compared. The improvement is evident, it shows that the
back-scatter problem of the ring laser gyros is negligible with a proper
analysis of the data, improving the performances of large scale ring laser
gyros, but also indicating that small scale instruments with sensitivity of
nrad/s are feasible.Comment: 9 pages and 7 figure
A Hopf Index Theorem for foliations
We formulate and prove an analog of the Hopf Index Theorem for Riemannian
foliations. We compute the basic Euler characteristic of a closed Riemannian
manifold as a sum of indices of a non-degenerate basic vector field at critical
leaf closures. The primary tool used to establish this result is an adaptation
to foliations of the Witten deformation method.Comment: 26 page
A fast pneumatic sample-shuttle with attenuated shocks
We describe a home-built pneumatic shuttle suitable for the fast displacement
of samples in the vicinity of a highly sensitive atomic magnetometer. The
samples are magnetized at 1 T using a Halbach assembly of magnets. The device
enables the remote detection of free induction decay in ultra-low-field and
zero-field NMR experiments, in relaxometric measurements and in other
applications involving the displacement of magnetized samples within time
intervals as short as a few tens of milliseconds. Other possible applications
of fast sample shuttling exist in radiological studies, where samples have to
be irradiated and then analyzed in a 'cold' environment.Comment: 3 pages and 3 figures; 2 additional pages (2 figures) as a
supplemental materia
The GINGER Project and status of the ring-laser of LNGS
A ring-laser attached to the Earth measures the absolute angular velocity of the Earth summed
to the relativistic precessions, de Sitter and Lense-Thirring. GINGER (Gyroscopes IN GEneral
Relativity) is a project aiming at measuring the LenseThirring effect with a ground based detector;
it is based on an array of ring-lasers. Comparing the Earth angular velocity measured
by IERS and the measurement done with the GINGER array, the Lense-Thirring effect can be
evaluated. Compared to the existing space experiments, GINGER provides a local measurement,
not the averaged value and it is unnecessary to model the gravitational field. It is a proposal,
but it is not far from being a reality. In fact the GrossRing G of the Geodesy Observatory of
Wettzell has a sensitivity very close to the necessary one. G ofWettzell is part of the IERS system
which provides the measure of the Length Of the DAY (LOD); G provides information on the fast
component of LOD. In the last few years, a roadmap toward GINGER has been outlined. The
experiment G-GranSasso, financed by the INFN Commission II, is developing instrumentations
and tests along the roadmap of GINGER. In this short paper the main activities of G-GranSasso
and some results will be presented. The first results of GINGERino will be reported, GINGERino
is the large ring-laser installed inside LNGS and now in the commissioning phase. Ring-lasers
provide as well important informations for geophysics, in particular the rotational seismology,
which is an emerging field of science. GINGERino is one of the three experiments of common
interest between INFN and INGV
Thermal Control of a Dual Mode Parametric Sapphire Transducer
We propose a method to control the thermal stability of a sapphire dielectric
transducer made with two dielectric disks separated by a thin gap and
resonating in the whispering gallery (WG) modes of the electromagnetic field.
The simultaneous measurement of the frequencies of both a WGH mode and a WGE
mode allows one to discriminate the frequency shifts due to gap variations from
those due to temperature instability. A simple model, valid in quasi
equilibrium conditions, describes the frequency shift of the two modes in terms
of four tuning parameters. A procedure for the direct measurement of them is
presented.Comment: 5 pages, 6 figures, presented at EFTF-IFCS joint conference 200
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