He-Ne Ring Laser Research Articles

A high precision VIS/NIR dynamic goniometer-spectrometer

We present a method for measuring the refractive index (RI) and spectral characteristics of transparent triangular prisms based on the minimum deviation technique. The proposed method has been developed to automatically measure RI simultaneously for three different wavelengths to determine the spectral dependence of RI. A high precision dynamic goniometer with a He-Ne ring laser and continuously rotating autocollimation mirror was used to implement the proposed method. A set of reference prisms made of optical glass were experimentally studied and the measurement uncertainty budget was estimated. The obtained values of the expanded measurement uncertainty did not exceed 4.6 × 10−6 for near-infrared and 1.2 × 10−5 for visible wavelength ranges with a coverage factor k = 2 (95% level of confidence). It is shown that this method can be used for high-precision measurements of the RI and determine the spectral characteristics.

Hysteresis of lock-in range in a He-Ne ring laser gyroscope.

In this paper, a hysteresis of the lock-in range in a He-Ne ring laser gyroscope is theoretically analyzed. We propose a new model accounting an additional coupling of the counterpropagating waves due to their diffraction on the gratings induced in the cavity mirrors. Numerical simulations in the proposed model show the existence of broad hysteresis areas of a lock-in range. Dependence of hysteresis on the pump excess above the threshold has been studied.

Compensation of the laser parameter fluctuations in large ring-laser gyros: a Kalman filter approach

He-Ne ring-laser gyroscopes are, at present, the most precise devices for absolute angular velocity measurements. Limitations to their performance come from the nonlinear dynamics of the laser. Following Lamb semiclassical theory, we find a set of critical parameters affecting the time stability of the system. We propose a method for estimating the long-term drift of the laser parameters and for filtering out the laser dynamics effects from the rotation measurement. The parameter estimation procedure, based on the perturbative solutions of the laser dynamics, allows us to apply Kalman filter theory for the estimation of the angular velocity. Results of a comprehensive Monte Carlo simulation and results of a preliminary analysis on experimental data from the ring-laser prototype G-Pisa are shown and discussed.

A 1.82 m2 ring laser gyroscope for nano-rotational motion sensing

We present a fully active-controlled He-Ne ring laser gyroscope, operating in square cavity 1.35 m in side. The apparatus is designed to provide a very low mechanical and thermal drift of the ring cavity geometry and is conceived to be operative in two different orientations of the laser plane, in order to detect rotations around the vertical or the horizontal direction. Since June 2010 the system is active inside the Virgo interferometer central area with the aim of performing high sensitivity measurements of environmental rotational noise. So far, continuous not attempted operation of the gyroscope has been longer than 30 days. The main characteristics of the laser, the active remote-controlled stabilization systems and the data acquisition techniques are presented. An off-line data processing, supported by a simple model of the sensor, is shown to improve the effective long term stability. A rotational sensitivity at the level of ten nanoradiants per squareroot of Hz below 1 Hz, very close to the required specification for the improvement of the Virgo suspension control system, is demonstrated for the configuration where the laser plane is horizontal.

Rotational sensitivity of the G-Pisa gyrolaser

G-Pisa is an experiment investigating the possibility of operating a high-sensitivity laser gyroscope with area less than 1 m2 for improving the performances of the mirrors suspensions of the gravitational wave antenna Virgo. The experimental set-up consists of a He-Ne ring laser with a 4-mirror square cavity. The laser is pumped by an RF discharge where the RF oscillator includes the laser plasma to reach a better stability. The contrast of the Sagnac fringes is typically above 50% and a stable regime has been reached with the laser operating in either single mode or multimode. The effect of hydrogen contamination on the laser was also checked. A low-frequency sensitivity, below 1 Hz, in the range of 10(-8)(rad/s)/square root(Hz) has been measured.

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.

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).

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.

T violation and microhertz resolution in a ring laser

A He-Ne ring laser has given the Earth-rotation-induced Sagnac frequency to a precision of 1 microHz, or 2 parts in 10(8), 2 x 10(-21) of the laser frequency. Because the beat frequency in a ring laser originates in either timereversal or (with a more complicated polarization geometry) parity-violating effects, such systems have the potential of detecting ultrasmall symmetry violations.

Mode coupling in a He-Ne ring laser with backscattering.

An alternative approach is proposed to discuss mode coupling in bidirectional ring lasers that is induced by backscattering. It is shown that various features can be simply discussed in terms of the mode structure of the corresponding passive ring cavity. The nature of the backscattering is found to play a crucial role in determining the normal-mode structure. For instance, we show theoretically that, for a rotating ring laser (gyro), the characteristics of frequency locking are already present in the passive-mode structure if the mode coupling has a dissipative nature, i.e., if the backscattering originates in localized losses. If, on the other hand, the backscattering has a conservative nature, i.e., originates in steps of the refractive index, a frequency splitting is found in the passive-mode structure, making so-called oscillatory instability possible. Experimental observations are reported to support this point of view. The recently reported \ensuremath{\pi}-phase jumps in He-Ne ring lasers are shown to fit naturally into this scheme. These jumps can be described as transitions between the normal modes of the passive ring cavity.

Reduction of the effects of backscattering in A HeNe ring laser by increased loss and gain

It has recently been suggested that some of the consequences of backscattering from one counter-propagating mode of a ring laser into the other mode can be reduced, without actually reducing the amount of backscattering, by increasing both the loss and the gain of the laser. The validity of this suggestion is demonstrated by experiment.

Observation of random π phase jumps in a ring laser with backscattering

We have observed jumps of ±π in the phase difference between the two counterpropagating modes of a HeNe ring laser, whenever the complex backscattering coefficients R 1, R 2 satisfy the condition R 1 + R ∗ 2=0. The experiments made use of two retro-reflectors that allowed light to be reflected back into the ring laser cavity with controllable amplitudes and phases. The phase jumps are usually accompanied by oscillatory instabilities of the two mode intensities. The observed behavior is found to be consistent with computer solutions of the coupled equations of motion.

Mode Interactions in Four-frequency Degeneracy-lifted Ring Lasers

Abstract A non-planar ring cavity, with a non-reciprocal bias in the form of the longitudinal Zeeman effect on the gain medium, has been used to demonstrate four-mode bidirectional operation in a He-Ne ring laser at 632·8 nm. It has also been shown that this ring system is sensitive to rotation.

Polarization Frequency Splitting in Non-planar Ring Laser Resonators

Abstract A non-planar ring cavity has been used to demonstrate polarization frequency splitting providing reciprocal bias for a multi-oscillator ring laser gyroscope. A bias of 94 MHz has been observed for a cavity with a longitudinal mode spacing (c/L) of 260 MHz. The bias agrees well with the passive cavity splitting predicted by a Jones matrix analysis of the cavity. The application of a non-reciprocal bias, in the form of the Zeeman effect on the gain medium, has demonstrated four-mode operation in a He-Ne ring laser operating at 632·8 nm.

Self-locked He-Ne ring laser

Experimental conditions necessary for self-pulsing to occur in a He-Ne ring laser are reported. These results are compared with predictions that are based upon theoretical models that have been presented in the literature. Good qualitative agreement is found in that theory and experiment both show that self-pulsing will only occur over a range of excitation. Quantitative results differed enough to indicate that additional refinement is needed even though the models have identified many of the important parameters involved.

リングレーザを用いた角度の測定

An experimental study for high precision digital angle measurement by using a He-Ne ring laser is described. The triangular ring laser, which is composed of an invar framework with a cavity length of 180 cm and two plasma tubes filled with 14 : 1 : 1 mixture of He : Ne20 : Ne22 discharged with current-stabilized power supplies is used. Angles (30°) of twelve sides constituting a polygon are measured applying the principle that the integral of beat signal of the ring laser is directly proportional to the angle of rotation of the ring laser. The dispersion of the measured values is found to be 10"-45" for 30°. It has become clear that it is important to supress fluctuation of cavity length much less than the present level and to operate on stable single mode for better accuracy.

Light drag in a ring laser: An improved determination of the drag coefficient

The light drag in a rotating fused-silica disk inserted in a He-Ne ring laser was measured at $\ensuremath{\lambda}=633$ nm and found to be ${\ensuremath{\alpha}}_{e}=0.5424$ with an rms error ($1\ensuremath{\sigma}$) of \ifmmode\pm\else\textpm\fi{}2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, including the known error sources. This constitutes a tenfold improvement in accuracy over a previous result. While the given error margin does not include the value given by the Lorentz drag in a linear arrangement, ${\ensuremath{\alpha}}_{\mathrm{LO}}=0.54182$, the measured difference of $2\ensuremath{\sigma}$ is deemed too small to claim a discrepancy.

Traveling-wave gas laser

The ratio of the clockwise to counterclockwise intensities in a multimode HeNe ring laser was measured as the strength of unidirectional coupling between the two intensities was varied. These results are compared to calculations based on a gain saturation with field coupling model which indicates that intensity ratios >102 are possible. With the addition of an etalon in the laser cavity, stable single-mode operation is observed.

High peak power and short pulses from a ring laser mode locked by internal modulation

Mode-locked unidirectional traveling-wave oscillation of a He-Ne ring laser is theoretically shown to be possible by internal loss or phase modulation. It should have a higher peak power and shorter pulses than the conventional laser systems.

角速度測定のためのHe-Neリングレーザの基礎実験

角速度測定のためのHe-Neリングレーザの基礎実験