High sensitivity tool for geophysical applications: a geometrically locked ring laser gyroscope.

We demonstrate that a middle sized 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, 1.60×1.60m 2, and it lies in a plane orthogonal to the Earth's 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. We verified that the prototype properties are compatible with the seismic requirements. The obtained long term stability is of the order of 3 nanorad/s, and the short term sensitivity is close to 2n a n o r a d/s⋅H z -1/2. These results are limited only by the noisy environment; our laboratory is located in a building downtown.

Analysis of 90 day operation of the GINGERINO gyroscope.

Gyroscopes IN GEneral Relativity (GINGER) is a proposed experiment with the aim of measuring in a ground laboratory the gravitoelectric and gravitomagnetic effects foreseen by general relativity through an array of ring laser gyroscopes. GINGERINO is a square ring-laser prototype that has been built to investigate the level of noise inside the Gran Sasso underground laboratory. GINGERINO has shown the advantage of the underground location. Now it provides suitable data for geophysics and seismology. Since May 2017, it has continuously acquired data. The analysis of the first 90 days shows that the duty cycle is higher than 95%, and the quantum shot noise limit is of the order of 10-10(rad/s)/Hz. It is located in a seismically active area, and it recorded part of the central Italy earthquakes. Its high sensitivity in the frequency band of fraction of hertz makes it suitable for seismology studies. The main purpose of the present analysis is to investigate the long-term response of the apparatus. Simple and fast routines to suppress the disturbances coming from the laser have been developed. The Allan deviation of the raw data reaches some 10-6 after about 106 s of integration time, while the processed data show an improvement of 1 order of magnitude. Disturbances at the daily time scale are present in the processed data, and the expected signal induced by polar motion and solid Earth tides is covered by those disturbances.

Analysis of 90 day operation of the GINGERINO gyroscope: publisher's note.

This publisher's note identifies a figure error in Appl. Opt.57, 5844 (2018)APOPAI0003-693510.1364/AO.57.005844.

A dynamic analysis of the LO noise transfer mechanism in a Rb-cell frequency standard.

Frequency noise of the local oscillator at even harmonics of the modulation frequency is known to contribute to the short-term instability of passive frequency standards. The mechanism by which this noise transfer takes place in Rb-cell standards is described here in a comprehensive approach that includes both signal theory methods and a time-dependent quantum mechanical analysis. The resulting calculated transfer coefficients for the various even harmonics are discussed in relationship with measured coefficients in an actual experiment.

Coherent multiwave heterodyne frequency measurement of a far-infared laser by means of a femtosecond laser comb.

We demonstrate the possibility of using a femtosecond laser to measure with high accuracy the frequency of a far-infrared (FIR) monochromatic source, such as an optically pumped molecular laser, by generating in a suitable mixer a signal in the radio-frequency region at the frequency difference between n steps of a femtosecond comb and the FIR source. All the couples of modes lying a distance of n steps from one another contribute coherently to the heterodyne signal. The technique has been tested up to 670 GHz.

Subnatural coherence effects in saturation spectroscopy using a single traveling wave.

We have performed zero-field level-crossing resonance measurements (nonlinear Hanle effect) in a metastable Ca atomic beam. By saturating the optical transitions (3)P(1,2) ? (3)S(1), for which the radiative linewidth is 10.5 MHz, we have recorded resonances corresponding to widths of about 31 kHz. The effect has been investigated as a function of the saturating-radiation intensity. The frequency jitter of the laser used in the measurements is about 40 times wider than the recorded widths.

Ramsey fringes in the nonlinear Hanle effect in a metastable atomic beam.

Evidence of coherence effects has been observed in the Zeeman sublevels by means of nonlinear level crossing in a metastable Ca beam with resonance width 3 orders of magnitude less than the radiative linewidth of the investigated transitions. By using two separate traveling waves, Ramsey-like fringes have been observed. The final measured widths are determined by the transit time, are weakly dependent on the magnetic-field inhomogeneities, and are independent of the natural width of the optical transitions and the laser bandwidth.

Evidence for laser cooling in a magnesium atomic beam.

Laser cooling in a Mg atomic beam is reported for the first time to our knowledge. Previous cooling experiments were performed by using visible or infrared lasers. The Mg atoms were cooled by using an intracavity frequency-doubled dye laser at 285 nm to reach the resonant (1)S(0)-(1)P(1) transition. Evidence of laser cooling was obtained even with the limited available laser power ( approximately 1-2 mW).