Short wavelength operation of a 10 m perimeter ring laser gyroscope.

We report on the operation of a 10 m perimeter, helium-neon based ring laser gyroscope on the 3s 2→2p 6 (611.8 nm) and 3s 2→2p 10 (543.4 nm) transitions of neon. Cavity Q factors of 1.5×1012 and 3.8×1011 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.

Gyroscopic performance and some seismic measurements made with a 10 meter perimeter ring laser gyro housed in the Ernest Rutherford building.

We describe the construction and operation of a large ring laser whose beam paths enclose an area of 6.25m2. 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 1.1×1012 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 7.9×10-12rad/s/Hz 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.

Sensing Earth rotation with a helium-neon laser operating on three transitions in the visible region.

We demonstrate an active Sagnac ring interferometer that operates on the previously unexploited 3s2→2p6 (611.8 nm), 3s2→2p7 (604.6 nm), and 3s2→2p8 (593.9 nm) neon transitions, in a helium-neon gain medium. The cavity was constructed using state-of-the-art ion-beam sputtered, ultralow-loss supermirrors designed to yield greater transmission loss at lower optical frequency, which partially compensates for the gain differential across the three transitions. For an optimized cavity fill of 0.3 mbar partial pressure of neon (50% Ne20 and 50% Ne22) and a total gas pressure of 2 mbar, for laser operation at 611.8 nm, the cavity Q is 1.2×1011, having a cold cavity ringdown time of 38 µs. The laser yielded a stable Sagnac frequency of 117.4 Hz due to the Earth's rotation. The usable gyroscopic sensitivity is determined to be 8.8×10-9 rad/s for a measurement time of 128 s.

Gyroscopic operation on the 3s2→2p10 543.3 nm transition of neon in a 2.56 m2 ring cavity.

We report the development and initial operation of a 6.4 meter perimeter laser gyroscope employing the 543.3 nm, 3s2→2p10 transition of neon. Employing fused silica based supermirrors yielding a cavity Q of 3.9×1011 and an inferred lock in threshold below 1 µHz, the gyroscope unlocked on the bias provided by Earth rotation alone with a measured Sagnac frequency of approximately 133 Hz, which is 16% larger than that of the 632.8 nm transition.

The Macek and Davis experiment revisited: a large ring laser interferometer operating on the 2s2 → 2p4 transition of neon.

We operate a large helium-neon-based ring laser interferometer with single-crystal GaAs/AlGaAs optical coatings on the 2s2→2p4 transition of neon at a wavelength of 1.152276 µm. For either single longitudinal- or phase-locked multi-mode operation, the preferable gas composition for gyroscopic operation is 0.2 and 0.3 mbar of 50:50 neon with total pressures between 6-12 mbar. The Earth rotation bias is sufficient to unlock the device, yielding a Sagnac frequency of approximately 60 Hz.

Sensing earth's rotation with a helium-neon ring laser operating at 1.15 µm.

We report on the operation of a 2.56 m2 helium-neon based ring laser interferometer at a wavelength of 1.152276 µm using crystalline coated intracavity supermirrors. This work represents the first implementation of crystalline coatings in an active laser system and expands the core application area of these low-thermal-noise cavity end mirrors to inertial sensing systems. Stable gyroscopic behavior can only be obtained with the addition of helium to the gain medium as this quenches the 1.152502 µm (2s4→2p7) transition of the neon doublet which otherwise gives rise to mode competition. For the first time at this wavelength, the ring laser is observed to readily unlock on the bias provided by the earth's rotation alone, yielding a Sagnac frequency of approximately 59 Hz.

Mode behavior in ultralarge ring lasers.

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.

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 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.