The Restraint Of The Common-mode Noise In The Atom Interferometry Gravimeter

Atom interferometer was invented more than twenty years ago. As a very precise measurement tool, the atom interferometer is developed rapidly in fields of fundamental research and technical applications. Based on the development of cold atom interferometer, atom gravimeter was invented. The atom gravimeter can be applied to the field of geological mapping, exploration, guidance, and fundamental physics research. Compared with a single gravimeter, the synchronous measurement with two gravimeters has a wider application, such as the investigation of gravity gradient changing and some other physical research.Our group started to develop an atom interferometry gravimeter since 2005, and have already developed several gravimeters. The synchronous working of two sets of gravimeters has already achieved. The main work of this paper is to investigate the restraint of the common-mode noise in two atom interferometers. The content includes synchronous operation of two gravimeters, the investigation of common-mode noise, and the methods of common mode noise restraint.The first chapter is the introduction of the paper. Firstly, we will introduce the application prospect of precision gravity measurement. And then, we describe the development status of gravity measurement and give the comparison of the performance of several gravimeters and demonstrate the development of cold atom gravimeter. Finally, the main work of this paper is summed up in this chapter.In second chapter, the theory and experiment of the cold atom interferometry gravimeter are introduced. The theoretical part includes the evolution of atoms in the optical field, and the related theory of the gravity measurement. The experimental part introduces the experiment device of two sets of atom gravimeters and the experiment results.In the third chapter, the controlling system of the cold atom interferometry gravimeter is described. The controlling system includes hardware and software. The time sequence of controlling is demonstrated in this chapter. Besides, the extending functions of the controlling program are also introduced.In the fourth chapter, we classify the noises by a noise analysis model, and the analysis of the common-mode noise. We analyze the influence of the atom interferometer’s phase from the phase noise. And the main parts of common-mode noise are demonstrated. In addition, the main source of non-common mode noise is introduced.The fifth chapter is the research on the restraint of the vibration noise, which is the one of the most important common-mode noise sources. Passive vibration isolation scheme and active vibration isolation scheme are two kinds of conventional vibration restraint schemes, which will be introduced in this chapter. Furthermore, we introduce vibration correction scheme to restrain vibration noise, and the experiment results would be present in the end of the chapter.In the sixth chapter, an algorithm which is immune to the common-mode noise was introduced. The key point is using the method of ellipse fitting to obtain the differential signal of two gravimeters. We also invent a new ellipse fitting method which is approached by minimizing the sum of squared differential noises in two gravimeters. Finally, we present the simulation and experiment results in different noises, and the comparison between the ellipse fitting and the sinusoidal fitting.The seventh chapter is the summary of this paper and the prospect of the future work.In summary, the restraint of common-mode noise in two atom gravimeters with excellent synchronization was investigated in this thesis. The repetition rate is 2.2Hz and the single point measurement time is 450ms. With the passive vibration isolation, the resolution of the upper and lower gravimeter is 1.9x10-7 g/(?) and 2.1×10-7 g/(?) respectively. If we only use the method of vibration correction, the sensitivity is comparable with the passive vibration isolation’s. The atom interferometer can still produce a good measurement result without any passive vibration isolation in some extremely noisy environments by using of the vibration correction scheme. Furthermore, we use ellipse fitting method and get the differential signal of two gravimeters without the influence of common mode noise. The ellipse fitting is used to analysis the differential signal when the earthquake come, and get a good measurement result.