Random walk reduction in dithered ring laser gyroscope.

We experimentally demonstrated that the random walk in a dithered ring laser gyroscope caused by lock-in crossing can be eliminated by lock-in error compensation. Computer simulations demonstrated the effectiveness of this method. The experimental results show that the random walk coefficient can be reduced as predicted. Furthermore, gyroscopes with different random walk performances can achieve nearly the same random walk level after compensation, illustrating that the quantum limit can be approached after removing the lock-in error.

Optically pumped NMR oscillator based on 131Xe nuclear spins.

A 131Xe nuclear magnetic resonance (NMR) oscillator can be used in the measurement of rotation rates, CPT and Lorentz violation tests, etc. To improve the measurement precision of devices based on a 131Xe NMR oscillator, its characteristics need to be fully understood. Under the conditions where the Zeeman interaction is much larger than the quadrupolar interaction, the characteristics of the 131Xe NMR oscillator involving the magnetic resonance, free induction decay, and closed-loop oscillation are investigated both experimentally and theoretically. The main findings are as follows. The 131Xe NMR oscillator consists of six oscillators, three of which can be directly observed by a magnetometer. When the polarization of the 131Xe spin ensemble can be described by a spin temperature, the ensemble exhibits both spin orientation and spin alignment. The spin alignment breaks the symmetry of the three main oscillators. The free induction decay signal of 131Xe depends on parameters such as the spin alignment and the driving magnetic field, which make the measurement of the relaxation time difficult. In the closed-loop mode under self-excitation, the 131Xe NMR oscillator may oscillate with more than one frequency at certain feedback gain and phase. If the quadrupole splitting is much smaller than the spin relaxation rate, then the 131Xe oscillator can be described by the Bloch equations, and the 131Xe oscillator will have a large amplitude. The oscillation frequency of the closed-loop oscillator depends on the quadrupole splitting, polarization, and various relaxation times, which should be considered in designing a high-precision NMR sensor. The results are significant for optimizing and improving the performance of the 131Xe NMR oscillator as a sensor for precision measurement.

Theoretical analysis on the rotation-induced frequency difference in ring lasers with coupled cavities.

We analyzed the effective scale factor of ring laser gyros with coupled cavities in a general way. The coupled cavities can be made of both an odd and even number of mirrors, or even fiber coil. Compared with the "zero-vector-area" design in previous publications, we use the propagation loss rather than transmittance and reflectivity of mirrors to characterize the coupled cavities, which are more universal and controllable. In addition, we found the area of the coupled cavities could further enhance the effective scale factor by 1+l/L, where l and L are the round-trip length of the ring lasers and the coupled cavity, respectively. Therefore, the scheme using coupled cavities to enhance the sensitivity is more practical. These findings are important to realize highly sensitive ring laser gyros.

Practical Considerations on the Multi-layer Mirrors for Superluminal Ring Laser Gyroscopes.

We have created a simple model to analyze the restrictions on superluminal ring laser gyroscopes arising from the absorption of coating materials. For a ring laser gyroscope with a cavity length of 15 cm, the scale factor enhancement is nearly impossible due to absorption from the high dispersion mirror. In order to obtain a practical superluminal ring laser gyroscope, the extinction coefficient of coating materials should be less than 1E-10, which is a challenge at present.

Research on the thermal relaxation effect of nonplanar four-frequency differential laser gyro.

The nonplanar four-frequency differential laser gyro (NFFDLG, also called ZLG in the United States) has many advantages, such as the absence of mechanical noise, a whole solid state, high stability of scale factor, and no time delay. Because of its excellent performance, NFFDLG is currently the subject of research. In this paper, the error induced by the thermal relaxation effect is investigated both theoretically and experimentally, and some methods and conclusions that could restrain this error effectively are proposed. The experiment data confirm reliably that NFFDLG has a thermal relaxation effect error during overturning. At the same time, it is pointed out that the error can be minimized by reducing the stop interval. Furthermore, since the sum frequency could be affected more seriously by the overturning thermal relaxation effect than the difference frequency could, the former one can be used as one more sensitive condition in actual applications. As far as we know, the overturning thermal relaxation effect was first investigated in China, which is even not mentioned publicly.