| In this thesis, the author firstly introduces some concepts concerning time and frequency, then describes principle of the up-to-now most precise Laser Cooling - Cesium Atomic Fountain Clock and its running process, also the basic knowledge of semiconductor lasers and laser frequency stabilizations.According to the demands of the Laser Cooling - Cesium Atomic Fountain Clock and realizing the shortage, which needs to be improved, in the original laser frequency stabilization system, the author analyzes the basic technology that was used in the new system, and then presents a new frequency stabilization technique of External Cavity Diode Lasers (ECDL): AOM Frequency Jump Saturated Absorption - Digital Lock.In the third chapter, the author describes the design process of the new technique. The optical part uses a pump-probe and reference light configuration. The two beams are detected by two photodiodes. The outputs of the photodiodes pass two-way I/V converters and an analog subtract device to get the saturated absorption signal from which major part of the Doppler background is removed. The microcontroller then sets the frequency driving AOM to let the shifted optical frequency to jump alternatively to either side of the desired saturated absorption peak. The difference of the signals on two sides is fed into a digital PI controller, and the output of the controller serves the ECDL to lock its frequency to the desired central frequency of the saturated absorption.Beat experiments with two sets of stabilized ECDL systems demonstrated that a frequency stability of 1.1E-10/1s and a frequency reproducibility of 6.3E-11 have been achieved with this new stabilization technique. In addition this system can re-lock automatically in 3 seconds after unlocked by external disturbances, such as acoustic or mechanical, and has realized a sub-continuous lock of 3 weeks. This stabilized ECDL system has met the requirements of the Cs fountain clock under construction. |
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