G. E. Stedman

Ring laser detection of rotations from teleseismic waves

Horizontal and vertical rotational components of teleseismic surface and body waves are detected by large ring laser gyroscopes. This is illustrated with records from magnitudes 7.0 and 7.3 events at distances of 31 deg. and 42.6 deg. respectively. Phase comparisons with synchronous linear seismometer records confirm the gyroscopic coupling.

Conventionality of synchronisation, gauge dependence and test theories of relativity

Abstract The formal and operational significance of the choice of clock synchronization in relativity is reviewed, along with the historical debate over the associated choice of the one-way speed of light. Kinematic test theories generalising special relativity are recast in a nonstandard synchronisation. In particular, the Mansouri-Sexl test-theory is generalised to avoid a conflict between its interpretation and its gauge choice. Corresponding adjustments to the interpretation of recent experimental tests of relativity are presented. A test-theory for local Lorentz invariance is derived for a noninertial observer in a space of arbitrary curvature using differential geometric techniques and the Frenet frame. The Sagnac effect in a ring laser is considered for bounding the parameters of this theory.

Design and operation of a very large ring laser gyroscope

The design and initial operation of a vertical square He-Ne ring laser G0 with a perimeter of 14 m is discussed. This builds on earlier demonstrations of the feasibility of large ring lasers (perimeter approximately 4 m) for single-mode gyroscope operation and with lesser pulling than navigation gyroscopes. With servoing of the rf excitation to yield single-mode operation, G0 gave a quality factor 1 x 10(12) and a Sagnac line with a frequency of 287.8 +/- 1.0 Hz induced by Earth rotation Omega(E). This has confirmed some vital questions over the feasibility of very large gyroscopes for geodetic measurements at the level of 10(-9) Omega(E).

Sideband analysis and seismic detection in a large ring laser.

Aring laser unlocked by the Earths Sagnac effect has attained a frequency resolution of 1 part in 3 × 10(21) and a rotational resolution of 300 prad. We discuss both theoretically and experimentally the sideband structure of the Earth rotation-induced spectral line induced in the microhertz-hertz region by frequency modulation associated with extra mechanical motion, such as seismic events. The relative sideband height is an absolute measure of the rotational amplitude of that Fourier component. An initial analysis is given of the ring laser record from the Arthurs Pass-Coleridge seismic event of 18 June 1994.

On the detectability of the Lense-Thirring field from rotating laboratory masses using ring laser gyroscope interferometers

The possibility of detecting the Lense–Thirring field generated by the rotating earth (also rotating laboratory masses) is reassessed in view of recent dramatic advances in the technology of ring laser gyroscopes. This possibility is very much less remote than it was a decade ago. The effect may contribute significantly to the Sagnac frequency of planned instruments. Its discrimination and detection will require an improved metrology, linking the ring to the celestial reference frame, and a fuller study of dispersion- and backscatter-induced frequency pulling. Both these requirements have been the subject of recent major progress, and our goal looks feasible.

Observable frequency shifts via spin-rotation coupling

The phase perturbation arising from spin-rotation coupling is developed as a natural extension of the celebrated Sagnac effect. Experimental evidence in support of this phase shift, however, has yet to be realized due to the exceptional sensitivity required. We draw attention to the relevance of a series of experiments establishing that circularly polarized light, upon passing through a rotating half-wave plate, is changed in frequency by twice the rotation rate. These experiments may be interpreted as demonstrating the role of spin-rotation coupling in inducing this frequency shift, thus providing direct empirical verification of the coupling of the photon helicity to rotation. A neutron interferometry experiment is proposed which would be sensitive to an analogous frequency shift for fermions. In this arrangement, polarized neutrons enter an interferometer containing two spin flippers, one of which is rotating while the other is held stationary. An observable beating in the transmitted neutron beam intensity is predicted.

Precision stabilization of the optical frequency in a large ring laser gyroscope

Pressure-induced fractional changes of 10(-7) in the geometry of a large He-Ne ring laser gyroscope induce backscatter phase changes and thus a fractional pulling of the Sagnac frequency of ~5 x 10(-3). To counter this, the optical frequency was stabilized against an iodine-stabilized laser with a high-finesse Fabry-Perot interferometer and piezoelectric control of the ring perimeter. This scheme, although limited in principle by residual geometric asymmetry and in practice by low beam powers (10 pW), stabilized the perimeter to 2.4 nm (6 x 10(-10) or 300 kHz for the optical frequency) and the Sagnac frequency to 100 parts per million over several days.

Selection rules for optical activity and linear birefringence bilinear in electric and magnetic fields

All independent geometric factors are derived for the possible polarisation dependence of optical activity and linear birefringence effects bilinear in a static electric and magnetic field, for fluids. The extension to oriented systems is illustrated. Differences between the methods used and results obtained with those of earlier workers are noted and where possible resolved. Several optical effects predicted to exist by earlier workers are shown to be forbidden, and vice versa. In particular the Jones birefringence should appear in E1/M1 coupling for all fluids, irrespective of the centrosymmetric or non-magnetic character of the system, and there exist field-dependent refractive index contributions which reverse with the direction of the light beam and are detectable by a ring laser.

Experiments with an 834 m2 ring laser interferometer

An ultralarge ring He–Ne ring laser gyroscope, UG-2, with area 834 m2 and dimensions 39.7×21 m2, has been built underground at Cashmere Cavern, Christchurch, New Zealand (latitude −43.575°). Earth rotation is sufficient to unlock it, giving a Sagnac frequency of 2.18 kHz. Supermirrors are used with transmission ∼0.18 parts per million (ppm) and optical loss unexpectedly high at ∼200 ppm per reflection. The cavity Q is 1.5×1012. Residual Sagnac frequency error caused by backscatter coupling is measured as 1000 s, mechanical movement of the mirror assemblies, which act to change the geometrical dimensions and tilt. At all averaging times the residual rotational noise is well above the li...

Design and initial operation of a 367-m2 rectangular ring laser.

The design and operation of a proof-of-principle rectangular He-Ne ring laser resonator with a cavity perimeter of 77.0 m and an area of approximately 367 m2 are described. With unevacuated beam lines this device gave an Earth-induced Sagnac frequency of 1513 Hz, with a relative Allan deviation over 1000 s down to 3 parts per million. The Earths rotation provided a bias that eliminated the lock-in susceptibility. The use of increased pressure in the plasma tube facilitated single-mode operation by increasing the homogeneous pressure-broadened linewidth.