ABSTRACT
By virtue of its good monochromaticity and coherence, laser is widely used in such fields as precision metrology, optical communication, optical frequency standards, high resolution spectroscopy, etc. For instance, in precision interference measurement, the laser wavelength is used as a “ruler” that uses the principle of optical interference to measure various kinds of physical quantities (e.g., length, displacement, velocity, etc.). So, the accuracy of the laser wavelength (or frequency) will directly influence the accuracy in measurement. In laser communication, in order to enhance its receiving sensitivity, generally the coherent heterodyne receiving method is adopted; whether the laser frequency is stable or not will directly influence the receiving quality. For this reason, if it is desired to use laser in the above-mentioned fields, not only is the laser required to implement single frequency output, but also the laser frequency itself is required to be stable. However, for ordinary freely operating lasers, affected by the operation environment and relevant factors, the laser output, as an irregularly fluctuating quantity varying with time, is often unstable. To make laser frequency stable, we have to resort to the frequency stabilizing technology. Hence frequency stabilization has become an indispensable means of modern precision measuring technology. This chapter will mainly describe the methods and principles of frequency stabilization of a number of commonly applied He-Ne lasers as well as several newly developed frequency stabilizing methods.
