358 research outputs found
Rotational sensitivity of the "G-Pisa" gyrolaser
G-Pisa is an experiment investigating the possibility to operate a high
sensitivity laser gyroscope with area less than for improving the
performances of the mirrors suspensions of the gravitational wave antenna
Virgo. The experimental set-up consists in a He-Ne ring laser with a 4 mirrors
square cavity. The laser is pumped by an RF discharge where the RF oscillator
includes the laser plasma in order to reach a better stability. The contrast of
the Sagnac fringes is typically above 50% and a stable regime has been reached
with the laser operating both single mode or multimode. The effect of hydrogen
contamination on the laser was also checked. A low-frequency sensitivity, below
, in the range of has been
measured.Comment: 6 pages, 6 figures, presented at the EFTF-IFCS joint conference 200
Interferometric length metrology for the dimensional control of ultra-stable Ring Laser Gyroscopes
We present the experimental test of a method for controlling the absolute
length of the diagonals of square ring laser gyroscopes. The purpose is to
actively stabilize the ring cavity geometry and to enhance the rotation sensor
stability in order to reach the requirements for the detection of the
relativistic Lense-Thirring effect with a ground-based array of optical
gyroscopes. The test apparatus consists of two optical cavities 1.32 m in
length, reproducing the features of the ring cavity diagonal resonators of
large frame He-Ne ring laser gyroscopes. The proposed measurement technique is
based on the use of a single diode laser, injection locked to a frequency
stabilized He-Ne/Iodine frequency standard, and a single electro-optic
modulator. The laser is modulated with a combination of three frequencies
allowing to lock the two cavities to the same resonance frequency and, at the
same time, to determine the cavity Free Spectral Range (FSR). We obtain a
stable lock of the two cavities to the same optical frequency reference,
providing a length stabilization at the level of 1 part in , and the
determination of the two FSRs with a relative precision of 0.2 ppm. This is
equivalent to an error of 500 nm on the absolute length difference between the
two cavities
A realistic inversion algorithm for magnetic anomaly data: the Mt. Amiata volcano test
The aim of this work is the formulation of a 3D model of the Mt. Amiata volcanic complex (Southern Tuscany)
by means of geomagnetic data. This work is shown not only as a real test to check the validity of the inversion
algorithm, but also to add information about the structure of the volcanic complex. First, we outline briefly the
theory of geomagnetic data inversion and we introduce the approach adopted. Then we show the 3D model of the
Amiata volcano built from the inversion, and we compare it with the available geological information. The most
important consideration regards the surface distribution of the magnetization that is in good agreement with rock
samples from this area. Moreover, the recovered model orientation recall the extension of the lava flows, and as a
last proof of validity, the source appears to be contained inside of the topographic contour level. The credibility of
the inversion procedure drives the interpretation even for the deepest part of the volcano. The geomagnetic signal
appears suppressed at a depth of about 2 km, but the most striking consequence is that sub-vertical structures are
found even in different positions from the conduits shown in the geologic sections. The results are thus in good
agreement with the information obtained from other data, but showing features that had not been identified, stressing
the informative power of the geomagnetic signal when a meaningful inversion algorithm is used
A sapphire monolithic differential accelerometer as core sensor for gravity gradiometric geophysical instrumentation
Gradiometric gravimetry is a survey technique widely used in geological structure investigation. This work demonstrates
the feasibility of a new class of low frequency accelerometers for geodynamics studies and space applications.
We present the design features of a new low noise single-axis differential accelerometer; the sensor is suitable
to be used in a Gravity Gradiometer (GG) system for land geophysical survey and gravity gradient measurements.
A resolution of 1 Eötvös (1 Eö=10−9s−2) at one sample per second is achievable in a compact, lightweight
(less than 2 kg) portable instrument, operating at room temperature. The basic components of the sensor are two
identical rigidly connected accelerometers separated by a 15-cm baseline vector and the useful signal is extracted
as the subtraction of the two outputs, by means of an interferometric microwave readout system. The structure will
be engraved in a monocrystal of sapphire by means of Computer-Numerically-Controlled (CNC) ultrasonic machining:
the material was chosen because of its unique mix of outstanding mechanical and dielectric properties
Developing fiber lasers with Bragg reflectors as deep sea hydrophones
The present paper will discuss the work in progress at the Department of Physics of the University of Pisa in collaboration
with the IFAC laboratory of CNR in Florence to develop pressure sensors with outstanding sensitivity
in the acoustic and ultrasonic ranges. These devices are based on optically-pumped fiber lasers, where the
mirrors are Bragg gratings written into the fiber core
A high sensitivity tool for geophysical applications: A geometrically locked Ring Laser Gyroscope
This work demonstrates that a middle size ring laser gyroscope (RLG) can be a
very sensitive and robust instrument for rotational seismology, even if it
operates in a quite noisy environment. The RLG has a square cavity, m, and it lies in a plane orthogonal to the Earth rotational axis.
The Fabry-Perot optical cavities along the diagonals of the square were
accessed and their lengths were locked to a reference laser. Through a quite
simple locking circuit, we were able to keep the sensor fully operative for 14
days. The obtained long term stability is of the order of 3~nanorad/s and the
short term sensitivity close is to 2~nanorad/sHz. These results
are limited only by the noisy environment, our laboratory is located in a
building downtown.Comment: 9 pages, 4 figures, 25 reference
Sulla determinazione della densità di Bouguer ottimale
Nella produzione di una carta di anomalia da dati di gravità la riduzione di Bouguer gioca
un ruolo fondamentale. La sottrazione del contributo topografico è in questo caso essenziale al fine di evidenziare le variazioni laterali di densità e la geometria delle strutture generatrici
di interesse geofisico. La correzione di Bouguer è fortemente dominata dalla scelta del valore della densità di riduzione che può tuttavia lasciare effetti topografici indesiderati nella mappa residua....
Length measurement and stabilization of the diagonals of a square area laser gyroscope
Large frame ring laser gyroscopes are top sensitivity inertial sensors able to measure absolute angular rotation rate below prad s-1 in few seconds. The GINGER project is aiming at directly measuring the Lense-Thirring effect with an 1% precision on an Earth based experiment. GINGER is based on an array of large frame ring laser gyroscopes. The mechanical design of this apparatus requires a micrometric precision in the construction and the geometry must be stabilized in order to keep constant the scale factor of the instrument. The proposed control is based on square cavities, and relies on the length stabilization of the two diagonals, which must be equal at micrometric level. GP2 is the prototype devoted to the scale factor control test. As a first step, the lengths of the diagonals of the ring cavity have been measured through an interferometric technique with a statistical accuracy of some tens of nanometers, and they have been locked to the wavelength of a reference optical standard. Continuous operation has been obtained over more than 12 h, without loss of sensitivity. GP2 is located in a laboratory with standard temperature stabilization, with residual fluctuations of the order of 1 C. Besides the demonstration of the control effectiveness, the analysis of the Sagnac frequency demonstrates that relative small and low-cost ring lasers (around one meter of side) can also achieve a sensitivity of the order of nrad s-1 in the range 0.01-10 Hz in a standard environment, which is the target sensitivity in many different applications, such as rotational seismology and next generation gravitational waves detectors
Geometrical scale-factor stabilization of square cavity ring laser gyroscopes
Large frame ring laser gyros performances are ultimately limited by the instabilities of their geometrical parameters. We present the experimental activity on the GP2 ring laser gyro. GP2 is a ring laser gyro devoted to develop advanced stabilization techniques of the ring cavity geometrical scale-factor. A method based on optical interferometry has been developed for canceling the deformations of the resonator. The method is based on the measurement and stabilization of the absolute length of the cavity perimeter and of the resonators formed by the opposite cavity mirrors. The optical frequency reference in the experiment is an iodine-stabilized He-Ne laser, with a relative frequency stability of 10-11. The measurement of the absolute length of the two resonators has been demonstrated up to now on a test bench. We discuss the experimental results on GP2: the present performances as a ring laser gyro and the stabilization scheme to be implemented in the near future
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