Experimental Research Of Delayed Self-heterodyne Beat Frequency For Laser Pulse

As a medium of coherent detection, optical beat frequency can measure tiny frequency difference in a very sensitive and simple way. From the moment of being introduced to the field of measurement, it has been applied to large dimension measurement without guidance and small dimension measurement with high accuracy. The critical technique of coherent detection is to use frequency-stabilized laser as the local oscillate source. However, the issues of laser frequency stabilization have been troubling researchers for a long time. The paper aims to discover a new method of coherent detection by using delayed laser pulse as the source of beat frequency, which can measure the frequency difference through one pulse only. Thus, the problem can be easily solved.Theoretically, the paper designs an optical delayed cavity. Based on lossy media amplifier theory, a theoretical mode is created to discuss the output characteristic of delayed laser pulse. Several elements that influence the attenuation of laser pulse are analyzed, such as pump power, initial luminous intensity and the pulse width.Experimentally, the single-longitudinal mode laser by twisted mode cavity is applied and the pulse width is compressed by Q switch. The laser pulse delay experiment has been carried on. In addition, the elements that influence the number of laser pulse, including pump power, transmission of output coupling mirror and laser pulse width are discussed as well. Using the delayed laser pulse we've got as the source of beating frequency, the experiment on the beat frequency of delayed laser pulse is done. While comparing the results of beating with different delayed pulse, we also discussed the characteristic of frequency shifting of delayed pulse.