Showing papers on "Ring laser gyroscope published in 1977"

Passive ring resonator laser gyroscope

Abstract: A new method of measuring inertial rotation is presented. It is based on the use of a passive ring resonator as the rotation sensing element and an external laser for measuring the difference between the clockwise and counterclockwise lengths of the resonator. Preliminary performance data is included.

System for circular and complex tomography

Abstract: A system for conducting circular as well as complex tomographic procedures utilizing apparatus which has no mechanical linkage between the X-ray source and the X-ray receptor. The path of travel of the X-ray source both circularly and linearly is sensed by electromagnetic radiation and more particularly by light radiation which is generated by a laser. The linear travel is sensed by means of reflected laser radiation directed to the X-ray source and fed to an interferometer. The circular travel, on the other hand, is sensed by means of a laser gyroscope also receiving light radiation from a laser. Optical energy sensing means is thus used to generate command signals which are coupled to respective drive motors which act to rotate and when desirable, translate the X-ray receptor so that its motion follows the motion, both orbital and linear, of the X-ray source for performing any desired type of tomographic procedure.

Dual mode laser optics control for ring laser gyro

Abstract: In a ring laser type gyro, laser optics adjustment means comprising a duo-mode bimorph device for separately controlling each of the optical length and alignment of the gyro laser optics.

Laser gyroscope output optics structure

Abstract: A four frequency laser gyroscope system having a rugged and compact output structure for producing output signals representing the frequency differences between counter-circulating wave pairs circulating as two beams within the gyroscope cavity. A partially transmitting dielectric mirror forms both one of the cavity reflectors and the means for extracting a small portion of each beam. The two extracted beams are combined on a beam splitter. Both the transmitted and reflected beams from the output of the beam splitter, each containing waves of all four frequencies, are utilized. Each resultant beam is then polarization discriminated to extract the desired signal content. The entire structure is adapted for rigid mechanical coupling and may be constructed to have a small size.

Phase-coded control for ring laser gyro

Abstract: In a laser gyro, laser optics adjustment means comprising a mirror within the laser optics of the gyro and mounted upon a three-terminal duo-mode bimorph device for duo-mode modulation of the laser optics. A two-stage differential amplifier is responsively coupled to a source of two mutually phase-coded reference signals for separately dithering each mode of the duo-mode bimorph device, each stage being further responsive to a mutually exclusive one of a first and second synchronously detected photodetector output of the laser gyro whereby closed loop control of the laser optics is effected.

Feedback system for a ring laser gyro

Abstract: In a ring laser gyroscope the residual "lock-in" which normally remains with an open loop dither system is overcome through the use of a dynamic feedback system between the output of the ring laser gyro and the dither rate input.

Ring laser gyroscope

Abstract: The invention is concerned with angular rate sensors, and particularly with ring laser gyroscopes which includes means for compensating for the effects of temperature gradients and residual lock-in. A ring laser gyroscope is provided which has a triangular block configuration, and which incorporates a triangular-shaped laser resonant cavity defined by three corner mirrors, including an output mirror. The ring laser gyroscope of the invention includes an optical wedge and a prism attached to its output mirror which permit the center of support of the gyroscope to be located in the plane of symmetry of the block. The gyroscope is mechanically vibrated about its center of gravity to prevent lock-in effects at low angular input rates. The construction of the gyroscope reduces temperature gradients across the plane of symmetry of the instrument, which temperature gradients produce spurious output signals in the absence of an input angular rate. The optical wedge and prism, together with an external corner cube retro-reflector, form an interferometer which provides compensation for the output signal of the gyroscope, enabling the gyroscope to produce an output free from the influence of the mechanical vibrations over a substantial angle, and which permits large angle low frequency mechanical vibrations to be introduced to prevent lock-in effects, which large angle low frequency vibrations have no tendency to cause residual lock-in effects to occur which produce non-linearities in the scale factor of the laser.

Laser gyroscope detector and path length control system

Abstract: A four frequency laser gyroscope system having parallel processing of path length control and detection signals. Two output signal beams each containing components of two of the four waves circulating in the laser cavity are shone upon separate detector diodes. The output signals from the diodes contain both high and low frequency components which are separated in a crossover circuit. The low frequency component is processed to control the optical path length while the high frequency component is processed to produce a digital signal representing the amount of rotation of the laser gyroscope cavity.

Multioscillator ring laser gyro output information processing system

Abstract: A four mode ring laser gyro has its four modes at different frequencies combined and applied to a single photo diode. The output from the photo diode is applied to a non-linear device, and the resultant sum and difference frequencies are applied to (1) a laser cavity length control circuit, (2) a rotation rate detection circuit, and (3) a rotation direction determination circuit. The cavity length control circuit operates by the determination of 100% modulation of one of the beat frequencies by a second one. The direction determination circuit utilizes the phase of an AC dithering power supply which varies the anode to cathode plasma current of the laser gyro.

Ring laser gyroscope having wedge desensitizing optical means

Abstract: A ring laser gyroscope having a triangular block configuration and means to dither the block about its line of symmetry. The triangular block is configured to be symmetrical about its axis of symmetry to reduce the temperature gradient across the instrument, which effect causes output signals in the absence of an input angular rate. An optical wedge attached to the output reflector of the triangular block and an external output prism form an interferometer by means of which the sensitivity of the device is reduced and the interferometer signal made equal and opposite to that of the laser cavity.

Miniature north reference unit

Abstract: The gyroscope operated in a strapdown mode and mounted on a float assembly with its spin axis extending in a vertical direction. The float assembly is free to rotate about any horizontal axis but is constrained from rotating about the vertical to assure an accurate azimuthal reference between the gyroscope and the case in which it is floating. The angle between an azimuthal reference line of the gyroscope and true north is obtained by measuring the amount of torque required to counteract precession of the gyroscope about a horizontal sensitive axis which would occur because of the horizontal component of the rate of rotation of the earth.

Differential Laser Gyro Development

Abstract: The Differential Laser Gyro (dilag) is a significant advancement in strapdown inertial guidance. Its four simultaneously oscillating modes allow it to retain the advantages inherent in a laser gyro without many of the drawbacks found in present two mode units. The DILAG concept employs two complete laser gyros operating in the same optical cavity. The gyros are distinguished from each other by their polarization state; one is right circularly polarized (RCP), while the other is left circularly polarized (LCP). Both gyros are biased out of their respective dead-band regions by the same Faraday cell. Because of their opposite polarization states, the gyros respond with equal but opposite frequency shifts to a given rotational input rate. When one gyro output is subtracted from the other, the result is a doubling of rate sensitivity combined with a cancellation of the common Faraday bias. Operated in this manner, the DILAG becomes insensitive to variations in the Faraday bias and thereby eliminates the usual requirements for Faraday cell stability. In addition the DILAG requires no dithering, either mechanical or electrical. This paper considers these points as well as a number of other special characteristics of the DILAG which offer significant improvements in gyro performance. Among those areas discussed are the reduction in shielding requirements, the elimination of all moving parts including those associated with cavity length control, and the advantages occurring in data collection and self check capability.

A high accuracy gyroscope readout test facility for the relativity gyroscope experiment

Abstract: We are building an apparatus for Earth-based testing of a gyroscope system to be used in a satellite test of general relativity. The immediate goal is a readout capable of measuring the direction of the gyroscope spin axis to an angular resolution of one arcsecond over a limited range. A combination of SQUID magnetometers and persistent current loops are used to measure the London moment of the spinning superconducting rotor levitated electrostatically. To obtain a trapped flux signal in the gyroscope sufficiently smaller than the London moment signal, the apparatus makes use of a new magnetic field shielding technique for obtaining large superconductor shielded regions below 10-7gauss.

New laser gyroscope using a passive ring resonator

Abstract: laser have been detailed previously.2 Briefly, a hydrogen halide laser (typically HBr) is used to excite a low pressure gas sample containing both the same hydrogen halide and CO, . Vibrational transfer to the CO, from the laser excited hydrogen halide, and, then, subsequent application ofa stimulating (or pumping) pulse at 9.6 or 10.6 pm causes inversion of the relevant 16 or 14 pm laser levels, respectively. A summary of typical operating parameters is given in Table I. Line by line tuning of the 16 pm laser was obtained with the cavity shown in Fig. 1. Because the 9.6 pm pulse was supplied to the cavity from an external single line CO, laser, both the 9.6 pm pumping transition and the 16 pm lasing transition could be varied independently. We learned that with a single, fixed P or R branch stimulating transition, numerous 16 pm P, Q , or R branch transitions could be tuned into oscillation. Thus, the CO, rotational manifold was completely thermalized during both the application of the stimulating pulse and the formation 16 pm pulse. The laser pulse energy in the strongest 16 pm lines was comparable to that extracted from a wavelength independent cavity. Byadjustinga number of laser design parame. ters chiefly oulput coupling, mode size, sample cell length and the gas pressure therein-we have substantially improved the optically pumped laser energy. The best result to date, which was obtained with a 40 cm length cell and 20 mJ of absorbed HBr laser energy, was 0.3 mJ.3 Efficiency arguments, which are based on our current understanding of the laser kinetics, indicate that further improvements in the pulse energy can be expected. Experiments with both the line selected 16 pm laser and a fluorescence cell containing HBr and CO, have yielded information on the gas kinetics in the optically pumped laser medium. Earlier measurements in the fluorescence cell showed that deactivation of the CO, 01'0 level by HBr is extremely fast, 6 x lo4 sec-' torr-'. Experiments with the line selective cavity have shown that the rate for the deactivation of the upper 16pm laser level by HBr, while fast, is still slower than the rate for rotational thermalization ofCO, , i.e. approximately IO6 sec-' torr-'. Finally. we are currently attempting to obtain

Possible Use of the Mach-Zehnder Heterodyne Interferometer As a Gyroscope

Abstract: The potential advantages of the Mach-Zehnder Heterodyne Interferometer as a rotation sensing device are discussed. Recently, a Mach-Zehnder Heterodyne Interferometer was described which allowed the direct reading of changes in the relative phase between the two beams. This was achieved by the use of a phase comparator that develops a voltage which is linear with increasing relative phase. The purpose of this note is to point out the potential advantages that such a device could have as a rotation sensor. Of course, the capability of a passive interferometer to sense rotations has been known since Sagnac's work. More recently, interest has centered on the ring laser gyro as an active interferometer. Both devices have disadvantages that limit their usefulness. The Sagnac Interferometer reflects rotational motion by a fringe shift which is proportional to the rate of rotation.

Laser Gyro Technology

Abstract: The technology of the laser gyro has advanced to where production of this unique gyro withlow cost and high performance is now possible. The technology of lifetime and its factorshave now shown operating lifetime capability in excess of 50,000 hours. The performancevariation with wavelength and size shows the wide range of parameters which must be con-sidered. The performance of the laser gyro in scale factor linearity varies from 0.1% in thesmall 9.8 cm 1.15p gyro to better than 0.0001% in the 43 cm 0.63p gyro. In similar fashionthe null stability and performance also varies over a range of 10 ° /hr to 0.01 ° /hr for thesame gyros, respectively. Other factors such as gas pressure and multi mode effects are alsodiscussed.IntroductionThe laser gyro has been in the research and development stage since 19621 and the firstdemonstration in 19632. In the years since the development of the technology to implementthis exciting concept to practical use as an inertial instrument has required an advancedtheoretical understanding and analysis of the He -Ne laser and associated extensive experi-mental investigations and advanced construction and assembly techniques to achieve lifetimeand low cost. In the past two years the experimental and theoretical results show that thisdevice will challenge conventional gyroscopes in many applications.The basic principal of the laser is quite simple, i.e., a closed path, rotating in inertialspace, will have a path length which is slightly larger in the direction of rotation andshorter when traveling around the path against the direction of rotation. This path differ-ence is proportional to the input rate. The laser gyro utlizes this phenomena to measureinertial motion by having two laser oscillators operating around the cavity. One of these isclockwise and one counter -clockwise. Since the frequency of the oscillator will adjust tothe path length the difference in frequency between the two oscillators is a direct and linearmeasurement of the inertial input rate.This represents perhaps the only method of sensing inertial rate which does not use storedenergy in a rotating or vibrating mass. The lack of this mass property has been viewed asone of the principal features of the laser gyro as it permits inertial rotation measurementswith virtually no g or g2 effects.The technologies which have been involved in these years in order to achieve a practicaldevice have required excellent analytical work3'