Search

A three-axis atomic magnetometer employing longitudinal field modulation is demonstrated theoretically and experimentally. The operational condition of this magnetometer is that the longitudinal z-component of the external magnetic field is dominant, which is achieved by applying a bias magnetic field. The longitudinal z-component of the external magnetic field is extracted from the modulation frequency, which tracks the resonance frequency, and the transverse x- and y- components are, respectively, obtained from the quadrature and the in-phase signals of a lock-in amplifier. Through feedback control, the magnitude and direction of an external magnetic field can be measured in real time, and an excellent orthogonality of the three-axis magnetometer response is obtained. By optimizing the parameters of this three-axis magnetometer, a longitudinal field sensitivity of 0.3 ${\rm{pT}/ \rm{Hz}}^{1/ 2}$ and a transverse field sensitivity of 2 ${\rm{pT}/ \rm{Hz}}^{1/ 2}$ are achieved.

Optically pumped rubidium atomic magnetometer with elliptically polarized light is demonstrated theoretically and experimentally. Compared with the conventional optical absorption detection mode, the sensitivity of atomic magnetometer for this detection mode can be improved by an order of magnitude under our experimental condition. Some parameters that influence the performance of this magnetometer is studied, which are the form of elliptically polarized light, the amplitude of exciting magnetic field, and the laser intensity. The sensitivity of 2.5 pT/√Hz is obtained when these parameters are optimized.

The performance of radio frequency (RF) exciting He-Ne laser is exposed. This text sets out from power circuit, aiming at providing the pumping of gain medium. In order to study the frequency characteristic of RF excitation in He- Ne laser, the frequency ranging from 300MHz to 700MHz is chose to test the discharge property of active medium. It also obtains the optimal RF frequency (432MHz) through experiment, which is important to the improved design of RF exciting He-Ne laser.

The performance of radio frequency (RF) exciting He-Ne laser is exposed. This text sets out from kinetics property of the electronics inside the high-frequency, aiming at getting the relationship between radio frequency and plasma energy. In order to study the frequency characteristic of RF excitation in He-Ne laser, the frequency ranging from 300MHz to 700MHz is chose to test the discharge property of active medium. It also obtains the optimal RF frequency (432MHz) through experiment, which is important to the improved design of RF exciting He-Ne laser.

This paper describes the design, operation and test results of a miniature low cost inertial measurement unit (IMU) that uses low cost dithered ring laser gyroscope and quartzes flexible accelerometer. The hardware configuration of the miniature low cost IMU is introduced, mainly including basic configuration, performance of the ring laser gyroscope and accelerometer. The alignment algorithm and integrated GPS/inertial Kalman filter algorithm are introduced. The static experiments, turntable experiments and outdoor vehicle experiments are performed. Experimental results are presented in this paper showing the performance of the miniature low cost IMU.

To avoid the lock-in effect, a body dither is introduced for the ring laser gyro (RLG). A dither feedback signal is necessary to control the dither drive signal. In the current dither control method, a piezoelectric or electromagnetic transducer is often used to obtain the dither feedback. The read-out signal of the RLG contains all dither-related information; hence, dither feedback can be obtained from the read-out signal, and external feedback can be reduced. A novel dither controlling method without external feedback is introduced in the present paper. How to control the dither amplitude and track the resonant frequency of the dither motor is described in detail. A comparative experiment is conducted between the old dither control method and the new one. Results show that the output of RLG using the new method has the same accuracy as that using the old method, aside from having more compact circuit dimensions.

The strap-down inertial navigation system (SINS), especially the SINS composed by dithered ring laser gyroscope (DRLG) is a kind of equipment, which providing high reliability and performance for moving vehicles. However, the mechanical dither which is used to eliminate the “Lock-In” effect can cause vibration disturbance to the INS and lead to dithering coupling problem in the inertial measurement unit (IMU) gyroscope triad, so its further application is limited. Among DRLG errors between the true gyro rotation rate and the measured rotation rate, the frequently considered one is the input axis misalignment between input reference axis which is perpendicular to the mounting surface and gyro angular rate input axis. But the misalignment angle between DRLG dither axis and gyro angular rate input axis is often ignored by researchers, which is amplified by dither coupling problem and that would lead to negative effects especially in high accuracy SINS. In order to study the problem more clearly, the concept of misalignment between DRLG dither axis and gyro angle rate input axis is researched. Considering the error of misalignment is of the order of 10 -3 rad. or even smaller, the best way to measure it is using DRLG itself by means of an angle exciter as an auxiliary. In this paper, the concept of dither axis misalignment is explained explicitly firstly, based on this, the frequency of angle exciter is induced as reference parameter, when DRLG is mounted on the angle exciter in a certain angle, the projections of angle exciter rotation rate and mechanical oscillation rate on the gyro input axis are both sensed by DRLG. If the dither axis has misalignment error with the gyro input axis, there will be four major frequencies detected: the frequency of angle exciter, the dither mechanical frequency, sum and difference frequencies of the former two frequencies. Then the amplitude spectrum of DRLG output signal obtained by the using LabVIEW program. if there are only angle exciter and the dither mechanical frequencies, the misalignment may be too small to be detected, otherwise, the amplitude of the sum and difference frequencies will show the misalignment angle between the gyro angle rate input axis and the dither axis. Finally, some related parameters such as frequency and amplitude of the angle exciter and sample rate are calculated and the results are analyzed. The simulation and experiment result prove the effectiveness of the proposed method..

This paper researched the fabrication of perovskite synrock by self-propagating high temperature synthesis (SHS) and the characterization of the products. This synthesis process is simpler, the fabricated synrock can immobilize waste loading up to 35wt% SrO with satisfied physical properties (density>4.2g•cm-3, open porosity

Lock-in phenomenon in ring laser gyroscopes is directly related to effective backscattering, which includes both backscattering and nonuniform loss. Effective backscattering often differs in different states and can only be reflected in a working state via online estimation in the working state. Moreover, effective backscattering can result in the intensity modulation of beams in the opposite directions. The effective backscattering parameters can be obtained by measuring the weak modulations in the intensity signals under different rotation rates and by using the curve-fitting method. This letter demonstrates the online estimation of backscattering.

In ring laser gyros (RLGs), dynamic lock-in, which results from information loss in the lock-in region, occurs when a constant sine bias is introduced. However, sampling some signals in the lock-in region for a particular duration allows the retrieval of lost information. It is demonstrated how dynamic lock-in and the flat region in the input-output curve near the zero angle rate can be eliminated after compensation.

A laser Doppler angular vibrometer using a He–Ne dual-frequency ring laser (DF-RL) is demonstrated. By detecting the interference signal of two beams which are diffracted by the surface of two gratings, the displacement of angular vibration can be measured. To our knowledge, this is the first time that a DF-RL has been utilized as the source of a Doppler angular vibrometer. It shows in theory and experiment that this dual-differential laser Doppler angular vibrometer possesses a high precision and can suppress the error in horizontal vibration at the same time, which can be applied to high-frequency microangular vibration measurement.

In this letter, the relationship between the change of the closed-loop optical path and the movement of two adjacent spherical mirrors in ring laser gyros is investigated by matrix optical approach. When one spherical mirror is pushed forward and the other is pulled backward to maintain the total length of the closed-loop optical path constant, an equivalent rotation of the closed-loop optical path is found for the first time. Both numerical simulations and experimental results show the equivalent rotation rate is proportional to the velocities of the mirrors’ movement.

The mechanical dithered ring laser gyro (MDRLG) has to go across lock-in region twice every dither cycle, thus the information loss is inevitable. According to the lock-in equation, the lock-in error can be expressed by observable signals. The lock-in error compensation of MDRLG based on synchronous filtering is demonstrated in this paper. The outputs of MDRLG and error accumulations are filtered synchronized to insure their alignment in the time domain. Experimental results show that the effect of lock-in compensation is improved.

To avoid lock-in phenomenon, a rotational oscillation is implemented in mechanically dithered ring laser gyros. This oscillation or dither is typically provided by a dither motor. The dither motor needs to be driven at the resonant frequency, so dither controlling systems must track the resonant frequency of dither motors. In this paper, a frequency track method based on phase sensitive detector technology is put forward and compared with the traditional selfoscillation method in details. In high-low temperature experiments (-40℃ to 60℃), this method and the traditional one are compared. The results show that the new method has the equivalent accuracy as the traditional one. But this method has more compact dimension, and the amplitude evaluation and noise injection are easier.

The lock-in effect can reduce the performance of ring laser gyros. The lock-in effect is a result of backscattering. Self-consistent equations for ring laser gyro show that the intensity of the opposite beams has AC modulation at the frequency of beat frequency signal because of the backscattering. The amplitude and phase of the AC modulations have important information about the backscattering. Comparing to the DC component in intensity signal, The AC components are much smaller, it is not suitable to measure the AC components directly using analog to digital conversion. A novel synchronous demodulation method is proposed which taking advantage of the heterodyne read-out signals in quadrature. The coupling modulation under different rotation rate is measured, experiments of this system show that this system works well and we can draw beneficial conclusion from the experiments.

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.

A miniaturized HeNe laser with intensity and frequency simultaneously stabilized is described. The laser uses a monoblock glass ceramics as its tube to construct an improved steady structure. The closed loop cavity length control system stabilizes its frequency and the discharge current regulating system stabilizes its intensity. The electronic system integrating power supply and stabilization system is designed within two small circuit boards. The laser tube and circuit boards are assembled into a small package with dimensions of 180 mm×100 mm×150 mm. The laser outputs s-polarized light at wavelength of 632.99 nm with power of 0.44 mW. Test results show that its frequency stability can reach 8.4×10(-11) (1s Allan variance over 3 h) and frequency reproducibility at 1.3×10(-8). The laser's intensity stability is 0.011% over 9 h.