An optical method for precision small-angle measurement based on CCD-area-based autocollimator is proposed in this article. The autocollimator utilizes CCD area—an interline CCD image sensor in a video camera as its detector. A collimated image is taken by the video camera and captured into the memory of a personal computer by an image board with high performance, then the image is transformed into a digital image and can be further processed by software with special arithmetic. A small angular displacement is magnified twice by the collimator objective with a long focal length and the camera lens of the video camera. By using a cold-light source and special data processing arithmetic, the measuring resolution of the autocollimator has been greatly improved. The method is proved to be reliable by a prototype experiment. Although some inexpensive materials were used in the experiment, two-axis angular displacement can be measured simultaneously and a measuring accuracy of 0.01 arcsec has been achieved. If some expensive materials with lower temperature expansion coefficient are used, a measuring accuracy of about 0.005 arcsec or a much higher measuring accuracy can be achieved. Until now, this has been the highest measuring accuracy.
We report several findings on the optical-axis perturbation of monolithic triaxial ring resonator. A criterion, C, which represents the mismatching error of the monolithic triaxial ring resonator, has been found out and it cannot be decreased by modifying the angles of the terminal surfaces or the terminal mirrors of the resonator. When C not equal 0, an optimization method to share the mismatching error C in some specific directions equally and simultaneously has been proposed. The interesting findings are important to cavity design, cavity improvement, and alignment of the monolithic triaxial ring resonator.
A new method to measure the spin polarization of optically pumped alkali-metal atoms is demonstrated. Unlike the conventional method using far-detuned probe light, the near-resonant light with two specific frequencies was chosen. Because the Faraday rotation angle of this approach can be two orders of magnitude greater than that with the conventional method, this approach is more sensitive to the spin polarization. Based on the results of the experimental scheme, the spin polarization measurements are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this approach.Since the ingenious idea of optical pumping was proposed by Kastler in 1950 1 , it has played an important role in atomic physics 2-4 . Optical pumping is typically used to polarize alkali-metal atoms. Once an ensemble of alkali metal atoms is polarized, many perfect physical properties can be observed 2 . As a result, optically pumped alkali-metal vapor has been widely used in a variety of significant areas, such as atomic magnetometers 5-9 , Faraday filters 10-12 , atomic clocks 13 , quantum memory and teleportation 14,15 , and nuclear magnetic resonance 16,17 . The spin polarization, which reflects the spin coherence of an atomic ensemble, is a vital parameter of optically pumped alkali-metal atoms. For example, the spin polarization directly determines the performance of atomic magnetometers and has an optimal value for an atomic magnetometer 6,8 , and it is also helpful for people to research and design Faraday filters by obtaining accurate knowledge of the spin polarization 12 . Therefore, it is essential to measure the spin polarization of alkali-metal atoms accurately.The spin polarization is usually determined by Faraday rotation using far-detuned light 18,19 . In such a measurement, for the D 1 line transition of alkali-metal atoms, the Faraday rotation angle θ is given by 19where l is the length over which the probe light interacts with the alkali-metal vapor, e is the electron charge, N is the number density of the alkali-metal vapor, m e is the electron mass, c is the speed of light, δ is the probe detuning from the D 1 line transition, and P is the spin polarization of the alkali-metal atoms. A necessary condition of equation (1) is that δ is much greater than the hyperfine splitting 19 . In this case, θ is scarcely sensitive to P, unless N is large enough. For the vapor number density of 10 11 to 10 12 cm −3 , as θ is usually only several milliradians 18 , it is difficult to obtain accurate knowledge of the spin polarization using this method. However, in many practical applications, alkali-metal vapor operating at near room temperature, which corresponds to the number density close to 10 11 cm −3 , has great advantages and has been widely utilized. For example, room temperature operation can simplify the structure and can reduce the energy consumption for atomic magnetometers, as indicated by the many reported room temperature atomic magnetometers 8,20 . Therefore, a sensitive metho...
To the best of our knowledge, the generalized ray matrix, an augmented 5×5 ray matrix for a spherical mirror reflection with all the possible perturbation sources including three kinds of displacements and its detailed deducing process have been proposed in this paper for the first time. Square ring resonators and monolithic triaxial ring resonators have been chosen as examples to show its application, and some novel results of the optical-axis perturbation have been obtained. A novel method to eliminate the diaphragm mismatching error and the gain capillary mismatching error in monolithic triaxial ring resonators more effectively has also been proposed. Both those results and method have been confirmed by related experiments and the experimental results have been described with diagrammatic representation. This generalized ray matrix is valuable for ray analysis of various kinds of resonators. These results are important for the cavity design, cavity improvement and alignment of high accuracy and super high accuracy ring laser gyroscopes.
This paper describes a novel approach for identifying the Z-axis drift of the ring laser gyroscope (RLG) based on genetic algorithm (GA) and support vector regression (SVR) in the single-axis rotation inertial navigation system (SRINS). GA is used for selecting the optimal parameters of SVR. The latitude error and the temperature variation during the identification stage are adopted as inputs of GA-SVR. The navigation results show that the proposed GA-SVR model can reach an identification accuracy of 0.000 2 ( • )/ h for the Z-axis drift of RLG. Compared with the radial basis function-neural network (RBF-NN) model, the GA-SVR model is more effective in identification of the Z-axis drift of RLG.
Articles you may be interested inA reference-beam autocollimator with nanoradian sensitivity from mHz to kHz and dynamic range of 107 Rev. Sci. Instrum. 84, 095007 (2013); 10.1063/1.4821653 Small angular displacement measurement based on an autocollimator and a common-path compensation principle Rev. Sci. Instrum. 84, 015108 (2013); 10.1063/1.4773004 A high-precision five-degree-of-freedom measurement system based on laser collimator and interferometry techniques Rev. Sci. Instrum. 78, 095105 (2007); 10.1063/1.2786272 Design and performance of a sub-nanoradian resolution autocollimating optical lever Rev. Sci. Instrum. 78, 035105 (2007); 10.1063/1.2714044 CCD-area-based autocollimator for precision small-angle measurement Rev.A temperature-controlled autocollimator with ultrahigh angular measuring precision is proposed in this article, which is different from our previous publication ͓J. Yuan and X. W. Long, Rev. Sci. Instrum. 74, 1362 ͑2003͔͒. The autocollimator consists of a zoom lens illuminating a charge-coupled device ͑CCD͒. This design provides a compact size and increased stability without compromising precision. Moreover, this design makes it possible to detect a target mirror with either plane reflectors or spherical reflectors. Devices for shock absorption and heat insulation were implemented to diminish external interferences. A special temperature-control system for the autocollimator is designed to control the temperature of the autocollimator. The temperature of the autocollimator fluctuates less than ±0.01°C. The CCD camera's noise is a fatal obstacle that prevents us from achieving an ultrahigh angular measuring precision. In this article, the influence of the CCD camera's noise on the measuring resolution is analyzed theoretically in detail. Based on the analysis, some special noise-suppressing methods to eliminate the influence of the CCD camera's noise are proposed. Both the influence of the CCD camera's noise and the noise-suppressing methods have not been discussed in our previous publication ͓J. Yuan and X. W. Long, Rev. Sci. Instrum. 74, 1362 ͑2003͔͒. By using the methods mentioned above, the measuring precision of the autocollimator has been greatly improved and the requirements on the external condition have been greatly reduced. The method is proved to be reliable by a prototype experiment. Two-axis angular displacement can be measured simultaneously and a measuring precision of 0.005 arcsec has been achieved, which is currently the highest measuring precision in the world.
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