RING LASER FOR PRECISION-MEASUREMENT OF NONRECIPROCAL PHENOMENA

We constructed a 0.75 m2, square-ring laser operating at the helium-ne on wavelength 633 nm (474 THz), for precision experiments in applied s ciences as well as for fundamental experiments in the physics of nonre ciprocal optical and other phenomena. High-quality mirrors and the abs ence of media, except for the He-Ne gas mixture in the beam, insure a high-quality factor of the cavity and low lock-in frequency. The Sagna c effect by the earth rotation sufficed to unlock the countercirculati ng modes, without the need to restore to dither, or other means of bia sing, thus providing a very stable bias with a stability of the order of 1 part in 10(9). Once the ring is un-locked by this means and is in single mode excitation, the response is extremely linear in any addit ional frequency, whether induced mechanically or via electromagnetic f ields; in the Fourier domain, all lines are equally affected by freque ncy pulling and by susceptibility changes. As a result, their relative positions are not affected, and their absolute frequencies may be cal ibrated from the earth rotational frequency. We observed a net line wi dth of 32 +/- 2 MHz. The center of the earth line is determined with a precision of about 1 mHz, that is, with a fractional precision of 1 M Hz/474 THz congruent-to 2 x 10(-18), which outclasses Mossbauer 1! an d maser 2! lines by several orders of magnitude. This implies that it is now possible to obtain accuracies of such additional effects of th e order of millihertz. We intend to exploit this extraordinarily high resolution in seismography, in particular shear waves, as well as in a number of physics experiments such as Fresnel drag.