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The results of studying the effect of filamentary striae with birefringence 3 to 15 nm/cm in sitall [glass-ceramic] SO-115M on the quality of manufacturing of optical components of ring lasers and the accuracy characteristics of laser gyroscopes based on them are presented. It is shown that the presence of streaks with stresses not exceeding 15 nm/cm in sitall SO-115M does not affect the manufacturing accuracy of the resonator optical circuit and its assembly quality. The streaks in the output mirror of a ring laser serve as a source of additional backscattering and can increase the lock-in zone width. Proper adjustment of the output mirror makes it possible to reduce the amount of scattering and minimize the growth of the lock-in zone in a laser gyroscope. It is shown that the accuracy of a laser gyroscope is determined by the quality of the mirror substrates, the body geometry, and the level of backscattering inside the resonator. [ABSTRACT FROM AUTHOR]

Intracavity phase interferometry is a powerful phase sensing technique using two correlated, counter-propagating frequency combs (pulse trains) in mode-locked lasers. Generating dual frequency combs of the same repetition rate in fiber lasers is a new field with hitherto unanticipated challenges. The large intensity in the fiber core, coupled with the nonlinear index of glass, result in a cumulative nonlinear index on axis that dwarfs the signal to be measured. The large saturable gain changes in an unpredictable way the repetition rate of the laser impeding the creation of frequency combs with identical repetition rate. The huge amount of phase coupling between pulses crossing at the saturable absorber eliminates the small signal response (deadband). Although there have been prior observation of gyroscopic response in mode-locked ring lasers, to our knowledge this is the first time that orthogonally polarized pulses were used to successfully eliminate the deadband and obtain a beat note. [ABSTRACT FROM AUTHOR]

Frequency lock-in-induced deadband phenomena are major problems of ring laser gyroscopes (RLGs), which deteriorate linear responses to changes in the applied rotation rate. In this work, the frequency lock-in phenomenon occurring in the RLG was successfully investigated by compensating for the Sagnac effect through frequency analysis using a newly defined error function. Integrative and generalized viewpoints from the analyzed results provide new possibilities for relevant performance improvements of optical gyroscopes, as well as a deeper understanding of locked states in principle aspects. [ABSTRACT FROM AUTHOR]

In sensors, the highest precision in measurements is given by vacuum fluctuations of quantum mechanics, resulting in a shot noise limit. In a Mach–Zenhder interferometer (MZI), the intensity measurement is correlated with the phase, and thus, the precision measurement ( Δ n ) is coupled with the phase resolution ( Δ φ ) by the Heisenberg uncertainty principle. Quantum metrology offers a different solution to this precision measurement using nonclassical light such as squeezed light or higher-order entangled-photon pairs, resulting in a smaller Δ φ and sub-shot noise limit. Here, we propose another method for the high precision measurement overcoming the diffraction limit in classical physics, where the smaller Δ φ is achieved by phase quantization in a coupled interferometric system of coherence de Broglie waves. For a potential application of the proposed method, a quantum ring laser gyroscope is presented as a quantum version of the conventional ring laser gyroscope used for inertial navigation and geodesy. [ABSTRACT FROM AUTHOR]

In order to stabilize the self-biasing state of a laser gyroscope, a dual-longitudinal-mode asymmetric frequency stabilization technique was studied. The special frequency stabilization is based on the accurate control of the intensity tuning curve in the prism ring laser. In this study, the effects of the ratio of the Ne isotopes, the inflation pressure, and the frequencies coupling on the intensity tuning curve in a laser gyro were examined. The profiles of the intensity tuning curve were simulated under the mixing ratios of Ne20 and Ne22 of 1:1 and 7:3, and the inflation pressures were 350 Pa, 400 Pa, and 450 Pa. The mixing ratio of Ne20 and Ne27 was dealt with similarly. The method for precisely adjusting the profiles of the intensity tuning curve was analyzed. The profiles were verified by experiments under different isotope ratios and pressures. Finally, based on a prism ring laser with an optical length of 0.47 m, the proposed frequency stabilization method was preliminarily verified. [ABSTRACT FROM AUTHOR]

In this paper, we present the experimental observation of simultaneous bi-directional superluminal lasing in a triangular ring cavity without gain competition and crosstalk as needed for realizing a gyroscope based on the Sagnac effect. The gain spectrum for each of the lasers is tailored to be a narrow dip on top of a broad gain using two stable isotopes of Rb. Specifically, we make use of 85Rb to produce a broad gain spectrum via the optically pumped Raman gain process and 87Rb to produce a narrow absorption spectrum via the optically pump Raman depletion process. A separate gain cell is used for the laser in each direction. Inferred from the simulation, the spectral sensitivity enhancements of the clock-wise and counter-clock-wise superluminal ring lasers are ∼362 and ∼505, respectively, with the imbalance attributed to differences in pump powers. [ABSTRACT FROM AUTHOR]

A ring laser gyroscope is an optical sensor based on the Sagnac effect. It has many outstanding advantages, such as a short start-up time, a high precision, a wide dynamic range and a stable scale factor. It is insensitive to accelerations and is in wide use in aircraft attitude control, north finding applications including navigation and space missions. The path length transducer in a ring laser gyroscope is required to stabilize the optical path of the laser beams in the cavity. The path length control transducer may tilt in complex environment, which will cause deformation of resonant optical path in resonant cavity and seriously influence the performance of ring laser gyroscope. Firstly, for the first time, finite element analysis software ANSYS was used to simulate and analyze the small deformation of ring laser gyroscope's grooved mirror in three directions under typical random vibrational spectra, their value were 2.08 " , 2.10 " and 1.30 " respectively, and the deformation in the diaphragm of resonant cavity was obtained by combining with matrix optical theory quantitatively. Secondly, the influence rule of different radius of curvature and isostructural parameters on the tilt of path length control transducer was sought through quantitative analysis. Finally, combining with the change law of axial displacement in literature [5], an evaluation criterion for optimization was given and the optimized parameters were listed for path length control transducer. The tilt was reduced to 0.33 " after optimization, which was about 21.4% of current structure. The axial displacement reached 3.89 um, which was 1.84 times of existing structure. The research in the paper could provide reference for the design of path length control transducer of ring laser gyroscope. [ABSTRACT FROM AUTHOR]

The paper is dedicated to Dr. James Grote from US Air Force Wright Patterson Laboratory, Dayton, Ohio, USA on his 62nd anniversary as well as taking retirement from the US Air Force Wright Patterson Laboratory, Ohio. It describes shortly his biography, family as well as the principal scientific achievements, science popularizing, collaborations, research organization as well as its applications. [ABSTRACT FROM AUTHOR]

The French physicist Georges Sagnac is nowdays frequently cited by the engineers who work on devices such as ring-laser gyroscopes. These systems operate on the principle of the Sagnac effect. It is less known that Sagnac was a strong opponent to the theory of special relativity proposed by Albert Einstein. He set up his experiment to prove the existence of the aether discarded by the Einsteinian relativity. An accurate explanation of the phenomenon was provided by Paul Langevin in 1921. [ABSTRACT FROM AUTHOR]

The semiconductor gain medium has rich non-linear dynamics and several internal parameters influence the generation and propagation of light through it. With the gain medium being an integral part of semiconductor ring laser gyroscope (SRLG) cavity, its parameters affect the overall performance of the gyro. The effect is further elevated in integrated SRLG due to stronger confinement of charge carriers and photons leading to a more intense interaction between them. In this paper, we evaluate the influence of semiconductor gain medium parameters such as gain saturation coefficient, linewidth, internal quantum efficiency etc. on the sensitivity of bulk fiber-optic SRLG. Ways of controlling these parameters and optimizing their values to enhance the performance of SRLG are also discussed. [ABSTRACT FROM AUTHOR]

Gyroscopes IN General Relativity (GINGER) is a proposal of an Earth-base experiment to measure the Lense-Thirring effect. GINGER uses an array of ring lasers, which are the most sensitive inertial sensors to measure the rotation rate of the Earth. GINGER is based on a three-dimensional array of large size ring lasers, able to measure the de Sitter and Lense-Thirring effects. The instrument will be located in the INFN Gran Sasso underground laboratory, in Italy. We describe preliminary developments and measurements. Earlier prototypes based in Italy, GP2, GINGERino, and G-LAS are also described and their preliminary results reported. [ABSTRACT FROM AUTHOR]

The scale factor correction characteristics of two ring laser gyroscopes of different sizes are investigated systematically in this paper. The variation in the scale factor can reach 144 or 70 ppm for square gyroscopes with arm lengths of 8.4 cm or 15.6 cm, respectively, during frequency tuning. A dip in the scale factor is observed at the line center of the gain characteristic for both gyroscope sizes. When a different longitudinal mode is excited, the scale factor behavior remains the same, but the scale factor values differ slightly from those derived from geometric prediction. The scale factor tends to decrease with increasing discharge current, but the sensitivity of the scale factor to variations in the excitation decreases with increasing discharge current. [ABSTRACT FROM AUTHOR]

To further improve ring laser gyroscope (RLG) bias stability, a multiple-point temperature gradient algorithm is proposed for RLG bias compensation in this paper. Based on the multiple-point temperature measurement system, a complete thermo-image of the RLG block is developed. Combined with the multiple-point temperature gradients between different points of the RLG block, the particle swarm optimization algorithm is used to tune the support vector machine (SVM) parameters, and an optimized design for selecting the thermometer locations is also discussed. The experimental results validate the superiority of the introduced method and enhance the precision and generalizability in the RLG bias compensation model. [ABSTRACT FROM AUTHOR]

We propose and analyze a superluminal ring laser gyroscope (RLG) using multilayer optical coatings with huge group delay (GD). This GD assisted superluminal RLG can measure the absolute rotation with a giant sensitivity-enhancement factor of ∼103; while, the broadband FWHM of the enhancement factor can reach 20 MHz. This superluminal RLG is based on a traditional RLG with minimal re-engineering, and beneficial for miniaturization according to theoretical calculation. The idea of using GD coatings as a fast-light medium will shed lights on the design and application of fast-light sensors. [ABSTRACT FROM AUTHOR]

Precision and generalization ability are the two main requirements for modeling the temperature drift of a Ring Laser Gyroscope (RLG). Traditional methods such as the least square fitting and artificial neural network cannot achieve the optimal performance for both aspects. To solve this problem, a novel modeling method based on particle swarm optimization (PSO) tuning support vector machine (SVM) with multiple temperature variables input is proposed. First, the temperature drift data for modeling is preprocessed by adaptive forward linear prediction (FLP) filter. Then, the SVM method is employed to construct the drift model and guarantee the generalization ability. And the PSO algorithm is used to tune the parameters of SVM and improve the precision of established model. The results of experiment validate the superiority of the proposed method in both aspects. The method has been practically applied to a high precision RLG position and orientation system. [ABSTRACT FROM AUTHOR]

Highlights: [•] Whole mathematical model of Vibration Isolation System (VIS) in DRLG IMU is built. [•] An effective design method of VIS based on motion decoupling is proposed. [•] Six degree of freedom (DOF) model of VIS is decoupled into six one DOF models. [•] Stiffness and damping parameters are optimized to meet the precision requirement. [•] A veritable VIS used in DRLG POS is developed as an instance. [ABSTRACT FROM AUTHOR]

With the fast development of the large ring laser gyroscope (RLG) technology in the last decades, promising applications in geophysics and geodesy (e.g. observations of high-frequency variations of Earth's rotation, Earth's tide tilt and seismic waves) have been realized by various groups with currently running large RLGs. In this letter, we point out that in a large number of previous tilt correction models a significant term is missing. This term is related with the Shida number l2 (called l2-term in the following) and has a contribution, which is comparable with that from high-frequency Earth rotation variations due to ocean tides, to the Sagnac frequency record of RLGs. This term has to be removed (as part of the tilt correction) from the raw data so that RLGs can efficiently be employed as Earth's rotation detectors. [ABSTRACT FROM AUTHOR]

In this paper the misalignment interrelationship of two adjacent spherical mirrors in a square ring laser gyro is investigated in details. The results show that optical beam path perturbations induced by the misalignment of one spherical mirror can be partly balanced by adjusting the misalignment of the other spherical mirror. Then the experimental data also show that the ray decentration-induced intensity attenuation of the laser is much severer than the ray tilting-induced. According to these characteristics, a real-time control system based on an improved angle controller is designed to eliminate mirror misalignment in terms of practical operation of ring laser gyros. In temperature experiments (-40 to 60°C), the optical intensity attenuation decreases from 37 to 14% with this system. [ABSTRACT FROM AUTHOR]

For improving the calibration precision of ring laser gyroscope (RLG) inertial measurement unit (IMU) with antivibration system, a novel integrated calibration method using a hybrid analytic/Kalman filter approach was proposed. An optimization analytic calibration method with four-direction rotations, based on three-axis turn table, was designed to coarsely calculate all the coefficients of RLG IMU mathematical error model. For further amending the remains of analytic calibration caused by an antivibration system disturbance and gyroscope drifts, a fine calibration method based on extended Kalman filter was proposed. It regarded the velocity errors as observation using a lever arm compensation technique. The experimental results show that the proposed integrated calibration method can improve the efficiency and precision of RLG position and orientation system which had been practically applied in airborne survey/mapping system. [ABSTRACT FROM PUBLISHER]

Recently, we have been investigating the development of a superluminal ring laser, where finely tuned anomalous dispersion leads to an enhancement in the sensitivity of the laser frequency to a change in the cavity length, by as much as six orders of magnitude, for applications such as hypersensitive rotation sensing and accelerometry, as well as for gravitational wave detection. For such a laser, as well as other lasers that are used for precision metrology, the effective dispersion – manifested in the manner in which the lasing frequency varies as a function of a change in the cavity length due to the index induced by the medium under saturated gain corresponding to steady-state lasing – is of utmost significance. In determining the effective dispersion, the role of inhomogeneous broadening (IB) must be taken into consideration carefully. In this work, we consider an inhomogeneously broadened gain medium in a single mode optical cavity, and study the effective dispersion experienced by the lasing field. It is well known that the steady state index for such a laser cannot be expressed analytically. Previous studies have employed approximate models to interpret the effective dispersion, in two limits: IB is much larger than homogeneous broadening (HB), and IB is insignificant compared to HB. Here, we use an iterative but quickly converging numerical code to determine the exact behavior of the effective dispersion under all conditions, and show that the results agree with the expected behavior in these two limits. This technique paves the way for taking into account the effective dispersion in any inhomogeneously broadened laser, including the superluminal laser, in determining accurately its sensitivity to change in cavity length, as well as it quantum noise limited linewidth. [ABSTRACT FROM AUTHOR]

This paper presents a newtype of strapdown north finder. A simplified configuration is proposed, including three parts: a pendulous force-feedback accelerometer, a ring laser gyroscope, and a single-axis rotating platform. The dynamic northfinding scheme of continuous rotation is adopted to eliminate the lock-in region of the laser gyroscope and to modulate the weak attitude signals; meanwhile the complex leveling process is avoided in this proposed configuration. To suppress the drift noises of the accelerometer and gyroscope, two digital lock-in amplifiers are used to extract the weak attitude signals. Simulation results show that the north finder can determine the heading angle in 72 s, when the rotating rate is 10°/s with the maximum heading error less than 1.0'; meanwhile the horizontal attitude angles as well as the constant drift noises of the inertial components could also be obtained. [ABSTRACT FROM AUTHOR]

The application areas of piezoelectric materials are expanding rapidly in the form of piezo harvesters, sensors and actuators. A path length controller is a high-precision piezoelectric actuator used in laser oscillators, especially in ring laser gyroscopes. A path length controller alters the position of a mirror nanometrically by means of a control voltage to stabilize the route that a laser beam travels in an integral multiple of laser wavelength. The design and verification of a path length controller performance requires long (up to 3 months), expensive and precise production steps to be successfully terminated. In this study, a combined computational–experimental design framework was developed to control, optimize and verify the performance of the path length controller, without the need for ring laser gyroscope assembly. A novel framework was structured such that the piezoelectric performance characteristics were calculated using finite element analysis. Then, a stand-alone measurement system was developed to verify the finite element analysis results before system integration. The final performance of the novel framework was verified by a direct measurement method called mode-scanning, which is founded on laser interferometry. The study is concluded with the explanation of measurement errors and finite element correlations. [ABSTRACT FROM AUTHOR]

Gyroscopes merit an undeniable role in inertial navigation systems, geodesy and seismology. By employing the optical Sagnac effect, ring laser gyroscopes provide exceptionally accurate measurements of even ultraslow angular velocity with a resolution up to 10 − 11 rad/s. With the recent advancement of ultrafast fibre lasers and, particularly, enabling effective bidirectional generation, their applications have been expanded to the areas of dual-comb spectroscopy and gyroscopy. Exceptional compactness, maintenance-free operation and rather low cost make ultrafast fibre lasers attractive for sensing applications. Remarkably, laser gyroscope operation in the ultrashort pulse generation regime presents a promising approach for eliminating sensing limitations caused by the synchronisation of counter-propagating channels, the most critical of which is frequency lock-in. In this work, we overview the fundamentals of gyroscopic sensing and ultrafast fibre lasers to bridge the gap between tools development and their real-world applications. This article provides a historical outline, highlights the most recent advancements and discusses perspectives for the expanding field of ultrafast fibre laser gyroscopes. We acknowledge the bottlenecks and deficiencies of the presented ultrafast laser gyroscope concepts due to intrinsic physical effects or currently available measurement methodology. Finally, the current work outlines solutions for further ultrafast laser technology development to translate to future commercial gyroscopes. [ABSTRACT FROM AUTHOR]

The main application of a ring laser gyroscope is navigation. It is currently the most widely used device for strapdown inertial navigation systems. However, it is also applicable for high-precision angle metrology systems. This paper discusses the properties of a laser dynamic goniometer (LDG) based on the ring laser gyroscope and designed for the calibration of optical polygons and digital angle converters, and for the measurement of angles between external mirrors (theodolite operating mode). We consider the main sources of uncertainty, such as the ring laser gyro bias due to an external magnetic field and the instability caused by the velocity of rotation along with applicable methods of their compensation. The reversal method providing separation of uncertainties of the LDG and the calibrated angle converter is analyzed in detail. The simplified cross-calibration method is also considered. The results of calibration of optical encoders of various designs—with and without their own rotors (on-axis and off-axis in Euramet terminology)—are presented. Some results of the dynamic goniometer for the measurement of angles between external mirrors are presented. It is shown that the LDG in this mode of operation demonstrates better accuracy than modern theodolites and total stations. [ABSTRACT FROM AUTHOR]

Absolute rotation rate sensing with extreme sensitivity requires a combination of several large scale gyroscopes in order to obtain the full vector of rotation. We report on the construction and operation of a four-component, tetrahedral laser gyroscope array as large as a five story building and situated in a near surface, underground laboratory. It is demonstrated that reconstruction of the full Earth rotation vector can be achieved with sub-arcsecond resolution over more than six weeks. [ABSTRACT FROM AUTHOR]

Large frame ring laser gyroscopes are top sensitivity inertial sensors able to measure absolute angular rotation rate below prad s−1 in few seconds. The GINGER project is aiming at directly measuring the Lense–Thirring effect with an 1% precision on an Earth based experiment. GINGER is based on an array of large frame ring laser gyroscopes. The mechanical design of this apparatus requires a micrometric precision in the construction and the geometry must be stabilized in order to keep constant the scale factor of the instrument. The proposed control is based on square cavities, and relies on the length stabilization of the two diagonals, which must be equal at micrometric level. GP2 is the prototype devoted to the scale factor control test. As a first step, the lengths of the diagonals of the ring cavity have been measured through an interferometric technique with a statistical accuracy of some tens of nanometers, and they have been locked to the wavelength of a reference optical standard. Continuous operation has been obtained over more than 12 h, without loss of sensitivity. GP2 is located in a laboratory with standard temperature stabilization, with residual fluctuations of the order of 1 °C. Besides the demonstration of the control effectiveness, the analysis of the Sagnac frequency demonstrates that relative small and low-cost ring lasers (around one meter of side) can also achieve a sensitivity of the order of nrad s−1 in the range 0.01–10 Hz in a standard environment, which is the target sensitivity in many different applications, such as rotational seismology and next generation gravitational waves detectors. [ABSTRACT FROM AUTHOR]

We propose a method to avoid the mode-locking problem in an ring laser gyroscope by restricting the lasing field inside the gyroscope to one direction only. Output from this unidirectional gyroscope is split into a reference field and a signal field, which is sent into a dispersive system so that it acquires an additional phase when its frequency changes because of the Sagnac effect. Angular velocity of absolute rotation is estimated by measuring the phase of the signal field. Noise properties of the dispersive system, created by using optomechanically induced transparency, are studied and the conditions for optimal performance of the gyroscope are derived. [ABSTRACT FROM AUTHOR]

Ring laser gyro (RLG) can work in mechanically dithered mode or rate-biased mode according to the working state of the inertial navigation system (INS). It can change from one mode to the other by receiving outer instructions. To evaluate the performance of RLG in rate-biased mode, an inertial measurement unit (IMU) based on RLG is installed on a dual-axis turntable, the turntable offers a constant angular velocity to the RLGs, in that way RLG can work in the rate-biased mode. A calibration method is proposed to calibrate the scale factor error, misalignments and constant bias of RLG in rate-biased mode, experiment results show that the differences of scale factor of the three gyros in two modes are 9 ppm, 7 ppm and 3.5 ppm, the constant biases of the three RLGs in rate-biased mode are also different from that in mechanically dithered mode with the difference of 0.017°/h, 0.011°/h and 0.020°/h, the input axis misalignment angle of RLGs in different modes also changed. What is more, a calculation method of angle random walk (ARW) of RLG in rate-biased mode is also presented. Experimental results show that the ARW of the RLG in rate-biased mode is about one third of that in mechanically dithered. [ABSTRACT FROM AUTHOR]

Inertial sensors are important at application level and also in fundamental physics. Ring laser gyroscopes, which measure angular rotation rates, are among the most sensitive ones. Large area ring laser reach sensitivities at the level of fractions of prad/s, allowing measurements of relevant geophysical signals. Improvements of a factor 10–100 would make these instruments able to measure general relativity effects; this is the goal e.g. of the GINGER project, an Earth based experiment aiming to test the Lense–Thirring effect with an accuracy of 1 % . However, the laser induces non-linearities, effects larger in small scale instruments. We discuss a novel technique to analyse data, able to reduce non-linear laser effects. We apply this technique to data from two ring laser prototypes, and compare the precision of the measurement of the angular rotation rate obtained with the new and the standard methods. We show that the back-scatter problem of the ring laser gyroscopes is negligible with a proper analysis of the data. These results not only allow to improve the performance of large scale ring laser gyroscopes but also pave the way to the development of small scale instruments with nrad/s sensitivity, which are precious for environmental studies and as inertial platforms. [ABSTRACT FROM AUTHOR]

Inertial sensors have a very large area of interest, and ring laser gyros, which measure angular rotation rate, are certainlyone of the main one in term of sensitivity, dynamic range and bandwidth. Large area ring laser gyros routinely are able to measure fractions of prad/s, with high duty cycle and bandwidth, providing fast, direct and local measurement of relevant geodetic signals as daily polar motion and Chandler Wobbler. However, it is well known that the dynamic of the laser induces non-linearities, and those effects are more evident in small scale instruments. Sensitivity and accuracy improvements are always worthwhile, and in general there is demand for high sensitivity environmental study and development of inertial platforms, were small scale transportable instruments should be used. We discuss a novel technique to analyse the data, aiming at studying and removing those not-linearities. The aresult of the nalysis applied to the data of the RLG GINGERINO will be shown [ABSTRACT FROM AUTHOR]

CONT17 is a campaign of continuous VLBI (Very Long Baseline Interferometry) sessions performed from 28th of November to 12th of December 2017. Telescopes from two legacy S/X networks were observing in parallel for 15 days. Additionally, the stations of the VGOS (VLBI Global Observing System) broadband demonstration network were participating in 5 consecutive sessions. The ring laser gyroscope "G" in Wettzell, an inertial sensor for Earth rotation variations, was also operating during the time of CONT17 and delivered stable and high quality measurements for that period. In this study, we investigate the Earth orientation parameters determined from the different networks individually, as well as solutions from combinations of the VLBI observations among each other and with the measurements of the Ring Laser. [ABSTRACT FROM AUTHOR]

Sagnac interferometers have established themselves firmly in the Geosciences, so that we can now begin to separate and mitigate error sources that are not related to the rotation sensing process from the Sagnac interferogram. As a result of that we were able to reduce the measurement error of the 16 m2 G ring laser of the Geodetic Observatory Wettzell by a factor of more than two. At the same time the residual sensor drift reduced significantly. Until now most of the investigations on large ring laser gyroscopes were dealing with a single component ring laser, orientated horizontally on the ground. Over the last two years we have constructed the 4 component ring laser structure, which is arranged in the form of an inverted tetrahedron with the tip in the ground. For the first time this arrangement can provide three dimensional rotation measurements with additional redundancy.On this road of a high resolution monitoring of a global measurement quantity (Earth rotation) with a local sensor (ring laser), we have encountered a number of serious challenges. This talk illustrates the recent progress in high resolution Sagnac Interferometry and its application to the Geosciences. [ABSTRACT FROM AUTHOR]

We have created a simple model to analyze the restrictions on superluminal ring laser gyroscopes arising from the absorption of coating materials. For a ring laser gyroscope with a cavity length of 15 cm, the scale factor enhancement is nearly impossible due to absorption from the high dispersion mirror. In order to obtain a practical superluminal ring laser gyroscope, the extinction coefficient of coating materials should be less than 1E-10, which is a challenge at present. [ABSTRACT FROM AUTHOR]

Periodic rotation noise in the outputs of multi-oscillator ring laser gyros (MRLGs) is investigated in this paper for the first time. It is proved theoretically and experimentally that noise is induced by the crosstalk between two beat-frequency signals, which are combined from the left and right circularly polarized counter-propagating beams in MRLGs. Theoretical analysis and experimental results also indicate that the fundamental frequency of this noise is equal to the frequency difference between the two beat-frequency signals and the amplitude of the fundamental component is proportional to the crosstalk ratio between the two beat-frequency signals. Further, the amplitude of the nth-order component is proportional to the nth power of the crosstalk ratio. [ABSTRACT FROM AUTHOR]

A helium–neon ring laser cavity is modified by employing variable coupled passive cavities to introduce anomalous dispersion. An equivalent model for the coupled cavities is proposed, and new equations are performed. Theoretical analysis of the parameters is presented in detail, and a novel iterative method is proposed. Gyros using this ring laser are shown in different sensitivity enhancements with limited broadened passive cavity line-width, and the minimal measurable rotation rate is analyzed. The related quantum noise limited line-width is found to be broadened with limitations, which mainly depend on the round trip loss. Fluctuations are induced to analyze parameter influences on enhancements, and a novel modification method concerning mirror reflectivity is proposed for experimental setups. Finally several practical considerations are generally discussed, and some suggestions are proposed for realization. This fast light induced enhancement can be important for present gyros based on a He–Ne ring laser. [ABSTRACT FROM AUTHOR]

We present the experimental test of a method for controlling the absolute length of the diagonals of square ring laser gyroscopes. The purpose of this is to actively stabilize the ring cavity geometry and to enhance the rotation sensor stability in order to reach the requirements for the detection of the relativistic Lense–Thirring effect with a ground-based array of optical gyroscopes. The test apparatus consists of two optical cavities 1.32 m in length, reproducing the features of the ring cavity diagonal resonators of large-frame He–Ne ring laser gyroscopes. The proposed measurement technique is based on the use of a single diode laser, injection locked to a frequency stabilized He–Ne/iodine frequency standard, and a single electro-optic modulator. The laser is modulated with a combination of three frequencies, allowing us to lock the two cavities to the same resonance frequency and, at the same time, to determine the cavity free spectral range (FSR). We obtain a stable lock of the two cavities to the same optical frequency reference, providing a length stabilization at the level of 1 part in , and the determination of the two FSRs with a relative precision of ∼2 · 10−7. This is equivalent to an error of on the absolute length difference between the two cavities. [ABSTRACT FROM AUTHOR]

Over the last two decades a series of large ring laser gyroscopes have been built having an unparalleled scale factor. These upscaled devices have improved the sensitivity and stability for rotation rate measurements by six orders of magnitude when compared to previous commercial developments. This progress has made possible entirely new applications of ring laser gyroscopes in the fields of geophysics, geodesy, and seismology. Ring lasers are currently the only viable measurement technology, which is directly referenced to the instantaneous rotation axis of the Earth. The sensor technology is rapidly developing. This is evidenced by the first experimentally viable proposals to make terrestrial tests of general relativistic effects such as the frame dragging of the rotating Earth. [ABSTRACT FROM AUTHOR]