The sensitivity achieved by large ring-laser gyroscopes will make it possible to detect faint relativistic effects related to the rotation of the Earth’s mass. This task requires a strict control of the ring cavity geometry (shape and orientation), which can be performed by a novel network of portable heterodyne interferometers, capable of measuring the absolute distance betweeen two retro-reflectors with a nominal accuracy better than 1nm. First steps have been taken towards the realization of this device and a starting prototype of distance gauge is under development and test.
This work describes the progress in the developing of a hydrophonic sensors array, based on fiber laser
technology, tailored for underwater acoustic surveillance of harbors, naval forces, and, in general, of maritime areas of
strategic relevance; the same apparatus can also find application for marine mammals coastline surveying, simply
addressing a suitable frequency detection band. The sensors are Distributed Bragg Reflectors Fiber Lasers. The laser
active medium is an Er<sup>+</sup> doped fiber included between two Bragg mirrors that are photo-imprinted through UV radiation
on the fiber. The acoustic water pressure variations produce a longitudinal strain on the fiber laser structure with a
consequent modulation of the emission wavelength. An in-fiber un-balanced Michelson interferometer transforms the
wavelength modulation into phase modulation, enhancing the detection sensitivity. An acousto-optic modulator,
mounted on one arm of the interferometer, generates a frequency carrier to allow conventional demodulation techniques.
This apparatus has demonstrated a noise-equivalent level of less than 1 mPa/(Hz)<sup>1/2</sup> in the 0.5-5 kHz frequency band.
Experimentations in marine environment of sensor arrays are in progress, and the first results obtained on a couple of
sensors written on a same fiber are presented.
An high sensitivity laser gyroscope is presented operating in a square cavity of side length of the order of 1 m
with a measured sensitivity limit at the level of 2 · 10<sup>-9</sup>(rad/s)/
√Hz. We report on the active stabilization of the
laser optical frequency which is mainly driven by the environmental thermal fluctuations and the experimental
results obtained with the active stabilization system are given. Finally the applications of this gyrolaser as an
high-sensitive tilt-meter in Virgo, the large-frame interferometer for gravitational waves detection, are discussed.
Here we report some initial results in the study of optical pumping and laser cooling of metastable Mg atomic beam. Eighty-five percent of optical pumping efficiency and laser cooling effect have been observed. We have successfully used frequency doubled diode laser in the experiments as a velocity analysis light source because diode laser is important for making a practical magnesium frequency standard.