Research On Automatic Control Of Laser Frequency And Process For Cold Atom Interferometry

The laser cooling and trapping of atoms are the hotspots of modern physics and they had given rise to more interests in physicists due to its physical significance and the possibility of wide applications in the future. In the experiments of atom interferometry, the process of atoms interferometry experiments needs a precise automatic controlling and data acquisition system. Also, the frequency of laser needs to be controlled precisely, including frequency shifting, frequency stabilization and phase locking. All of these are the key techniques of atom interferometry, and they are and critical to the experiments final performance. Designing of the laser frequency and experiment process controlling system with high speed, high accuracy and high performance have the great significance to the development of laser cooling and atom interferometry. With this purpose, we chose designing of automatic controlling system of laser frequency and process for cold atom interferometry as the research subject. Fabrics of this dissertation are as follows.In chapter1, a brief introduction to the historical background, development and current applications of cold atom interferometry is given. Also, the background and surveys of three main techniques of laser frequency, including frequency shifting, frequency stabilization and phase locking, is given. The significance of high performance laser frequency and process automatic controlling system is explained.In chapter2, after a brief introduction of each part of the experiment device, the principals and the design of the process controlling and data acquisition system are described in details. Finally, its performance and applications are given. The applications proved that the system has the complete functions and the accuracy meets the experiments demands.In chapter3, the demands of laser frequency shifting and the various current methods are analyzed firstly, and the principals of direct digital synthesize (DDS) are presented. Then the design of the frequency shifting system based on DDS is described. Specially the design of hardware, software and the communication module between DDS and the superior computer are described in details. Finally, its performance and applications are given. It is shown that the performance of atom cooling and trapping based on DDS has been improved markedly in comparison with the technique based on voltage controlled oscillator.In chapter4, the demand of laser frequency stabilization and various techniques of frequency stabilization are analyzed firstly. It is pointed that the mode hopping is the main obstacle of long term stability of laser and the efficiency of the cold atom experiments. Then, after a brief introduction of mode hopping, a new suppressing method for mode hopping based on the periodical detection of mode boundary is presented. The design of a long-term frequency stabilization system based on this method is described in details. Finally, its performance and applications are given. The performance shows that the consecutive duration of stabilization of non-antireflection-coated diode laser can be extend to almost400hours by this system. This is a significant improvement of extended cavity diode lasers frequency stabilization system.In chapter5, various schemes and their pros and cons for Raman pulse generation in atom interferometry are given firstly, with the explanation that phase locking is the key technique of atom interferometry. Then a technique of all digital optical phase locking based on field programmable gate array (FPGA) is presented. The detail design and implementation is described in emphasis, including the innovative design of digital loop filter. All digital optical phase locking loop is implemented for the first time in the world. Finally, its performance and applications are given.In chapter6, a summary of the work achieved in this thesis and an outlook is given.