Noise Level of a Ring Laser Gyroscope in the Femto-Rad/s Range.

Absolute angular rotation rate measurements with sensitivity better than prad/s would be beneficial for fundamental science investigations. In this regard, large frame Earth based ring laser gyroscopes are top instrumentation as far as bandwidth, long-term operation, and sensitivity are concerned. Here, we demonstrate that the GINGERINO active-ring laser upper limiting noise is close to 2×10^{-15} rad/s for ∼2×10^{5} s of integration time, as estimated by the Allan deviation evaluated in a differential measurement scheme. This result is more than a factor of 10 better than the theoretical prediction so far accounted for ideal ring lasers shot-noise with the two beams counterpropagating inside the cavity considered as two independent propagating modes. This feature is related to the peculiarity of real ring laser system dynamics that causes phase crosstalking among the two counterpropagating modes. In this context, the independent beam model is, then, not applicable, and the measured noise limit falls below the expected one.

Radial distribution gain at 633 nm in a He-Ne RF-excited small bore discharge.

Devices as large as ring laser gyroscopes (RLGs) for fundamental physics and geophysics investigation are currently run by means of radio frequency (RF) power supply systems. This is not the standard method to supply a gas laser, which typically is powered by a DC system. In literature, RF power supply lasers were studied several years ago, and to correctly understand the behavior of devices such as RLGs, a more detailed study has been pursued. Detailed study of the radial distribution of the optical gain of a He-Ne discharge cell in function of gas pressure and radio frequency (RF) power supply will be illustrated, discussed, and compared with existing literature. The presented analysis demonstrates that it is possible to optimize ring laser gyroscope (RLG) operation with a proper choice of gas pressure and power level of the RF power supply. Accordingly, we have been able to establish transversal and longitudinal single-mode operation of our prototype GP2.

Monitoring Local Earthquakes in Central Italy Using 4C Single Station Data.

In this study, performed on a set of twenty-two earthquakes that occurred in central Italy between 2019 and 2020, we will explore the possibility to locate the hypocenter of local events by using a ring laser gyroscope observing the vertical ground rotation and a standard broadband seismometer. A picking algorithm exploiting the four components (4C) polarization properties of the wavefield is used to identify the first shear onset transversely polarized (SH). The wavefield direction is estimated by correlation between the vertical rotation rate and the transverse acceleration. The picked times for Pg and Sg onsets are compared to the ones obtained after manual revision on the GIGS station seismometer. The results are compared with the location provided by the national monitoring service of the INGV.

Compensation of the laser parameter fluctuations in large ring-laser gyros: a Kalman filter approach.

He-Ne ring-laser gyroscopes are, at present, the most precise devices for absolute angular velocity measurements. Limitations to their performance come from the nonlinear dynamics of the laser. Following Lamb semiclassical theory, we find a set of critical parameters affecting the time stability of the system. We propose a method for estimating the long-term drift of the laser parameters and for filtering out the laser dynamics effects from the rotation measurement. The parameter estimation procedure, based on the perturbative solutions of the laser dynamics, allows us to apply Kalman filter theory for the estimation of the angular velocity. Results of a comprehensive Monte Carlo simulation and results of a preliminary analysis on experimental data from the ring-laser prototype G-Pisa are shown and discussed.

Deep underground rotation measurements: GINGERino ring laser gyroscope in Gran Sasso.

GINGERino is a large frame laser gyroscope investigating the ground motion in the most inner part of the underground international laboratory of the Gran Sasso, in central Italy. It consists of a square ring laser with a 3.6 m side. Several days of continuous measurements have been collected, with the apparatus running unattended. The power spectral density in the seismic bandwidth is at the level of 10-10 (rad/s)/Hz. A maximum resolution of 30 prad/s is obtained with an integration time of few hundred seconds. The ring laser routinely detects seismic rotations induced by both regional earthquakes and teleseisms. A broadband seismic station is installed on the same structure of the gyroscope. First analysis of the correlation between the rotational and the translational signal is presented.

Rotational sensitivity of the G-Pisa gyrolaser.

G-Pisa is an experiment investigating the possibility of operating a high-sensitivity laser gyroscope with area less than 1 m2 for improving the performances of the mirrors suspensions of the gravitational wave antenna Virgo. The experimental set-up consists of a He-Ne ring laser with a 4-mirror square cavity. The laser is pumped by an RF discharge where the RF oscillator includes the laser plasma 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 in either single mode or multimode. The effect of hydrogen contamination on the laser was also checked. A low-frequency sensitivity, below 1 Hz, in the range of 10(-8)(rad/s)/square root(Hz) has been measured.

Measurement of the optical parameters of the Virgo interferometer.

The Virgo interferometer, aimed at detecting gravitational waves, is now in a commissioning phase. Measurements of its optical properties are needed for the understanding of the instrument. We present the techniques developed for the measurement of the optical parameters of Virgo. These parameters are compared with the Virgo specifications.