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We report on the operation of a 10 m perimeter, helium-neon based ring laser gyroscope on the 3 s 2 →2 p 6 (611.8 nm) and 3 s 2 →2 p 10 (543.4 nm) transitions of neon. Cavity Q factors of 1.5×10 12 and 3.8×10 11 are obtained for 611.8 and 543.4 nm operation, inferred from measured ring-down times of 485 and 110 μs, respectively. For Sagnac frequencies, due to Earth rotation, of 205.14 and 230.96 Hz, minimum resolvable rotation rates of 80 and 226 prad/s are achieved for integration times of around 100 s. While environment limited performance is achieved for operation at 611.8 nm, it is found that a restrictive gas pressure regime must be utilized for the 543.4 nm lasing wavelength. As a consequence, the output photon count is low, which limits its intrinsic sensitivity for rotation rate measurements.

We describe the construction and operation of a large ring laser whose beam paths enclose an area of 6.25 m 2 . The gyroscopic performance of this large laser interferometer was determined using laser operation at a wavelength of 632.8 nm. The laser cavity Q was inferred to be 1.1×10 12 via a measured ring-down time of 375 µs, and the measured Sagnac frequency is 198.40 Hz due to Earth's rotation. The measured experimental sensitivity to rotation achieved is 7.9×10 -12 r a d / s / H z at an averaging interval of 512 s (being limited primarily by ambient building noise). The observation of microseismic activity in the 200 mHz region as well as local earthquakes is discussed.

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.

Large ring lasers have exceeded the performance of navigational gyroscopes by several orders of magnitude and have become useful tools for geodesy. In order to apply them to tests in fundamental physics, remaining systematic errors have to be significantly reduced. We derive a modified expression for the Sagnac frequency of a square ring laser gyro under Earth rotation. The modifications include corrections for dispersion (of both the gain medium and the mirrors), for the Goos-Hänchen effect in the mirrors, and for refractive index of the gas filling the cavity. The corrections were measured and calculated for the 16  m 2 Grossring laser located at the Geodetic Observatory Wettzell. The optical frequency and the free spectral range of this laser were measured, allowing unique determination of the longitudinal mode number, and measurement of the dispersion. Ultimately we find that the absolute scale factor of the gyroscope can be estimated to an accuracy of approximately 1 part in 10 8 .

In ring laser gyroscopes, backscatter coupling between the counterpropagating beams leads to systematic errors in measured rotation rates. We show the errors can be derived from the nearly independent optical frequency perturbations of the separate beams. In a process of double backscatter each beam is scattered first into the other beam direction, then rescattered back into itself, giving phase and amplitude perturbations. The analysis proceeds from a purely passive ring cavity, through inclusion of a gain medium and gain saturation. The rotation rate errors may be estimated and corrected from the modulations of the counterpropagating beams. The method is demonstrated with real data.

A significant operational difficulty with very large ring laser gyroscopes is the length of time required to achieve the desired single-mode configuration. A control technique has been developed where the order of mode splitting between corotating beams is alternated. Theoretical advantages to this are the elimination of noise caused by variations in perimeter and systematic error caused by Adler pulling. External seeding of mode configurations has been proposed to allow the technique to work fast enough to eliminate known sources of perimeter perturbations. While investigating the intensity requirements for this concept, we found that the operating mode of a large ring laser can be successfully self-seeded with seed beams of near (6±3) single photon cavity mode population.

Contrary to expectations based on mode spacing, single-mode operation in very large He-Ne ring lasers may be achieved at intracavity power levels up to approximately0.15 times the saturation intensity for the He-Ne transition. Homogeneous line broadening at a high total gas pressure of 4-6 Torr allows a single-peaked gain profile that suppresses closely spaced multiple modes. At startup, decay of initial multiple modes may take tens of seconds. The single remaining mode in each direction persists metastably as the cavity is detuned by many times the mode frequency spacing. A theoretical explanation requires the gain profile to be concave down and to satisfy an inequality related to slope and saturation at the operating frequency. Calculated metastable frequency ranges are > 150 MHz at 6 Torr and depend strongly on pressure. Examples of unusual stable mode configurations are shown, with differently numbered modes in the two directions and with multiple modes at a spacing of approximately 100 MHz.

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 Earth's 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.