The Development Of Far-infrared HCN Two Color Laser System And The Study Of Intermediate Frequency Control On EAST

In the tokamak fusion device of plasma,electron density is an important physical parameter to measure the various physical phenomenon of plasma.Far infrared interferometer has been widely used in measurement of electron density of plasma.The optical configuration of the interferometer is the Mach-Zehnder interferometer type,there must be an intermediate frequency(IF)required deriving from heterodyne detection.The intermediate frequency is usually generated by rotating grating or dual laser system.For the rotating grating,the intermediate frequency is mainly realized by mechanical rotating parts.Although the method is simple and easy to operate,the stability of the intermediate frequency signal is poor and the modulation frequency is limited,which leads to the low time resolution of the interferometer.In view of the long pulse running characteristics of EAST devices and the improvement of future experimental parameters,the far-infrared HCN laser interferometer system must provide continuous,stable and reliable electron density feedback signals,and have high temporal resolution for rapid change of electron density and perturbation measuring.Therefore,the development of two color laser system to generate stable megahertz IF signal s,The time resolution of interferometer is greatly improved.In this paper,the hardware system of the two color laser is developed and the design idea of the IF and the power control are put forwarded based on the technology and principle of the HCN dual color laser system.The programming and design of the IF control software are finished,simultaneously,the IF output characteristic has been studied.According to the adjustment of the current experiment,the main components of the interferometer system are designed and reconstructed,including the reconstruction of the optical path,the improvement of the resonator,and the upgrade of the rotating grating.The experimental results show that the different IF signals(0.8MHz~6MHz)are obtained successfully adjusting the cavity length,and the cavity length is changed 10?m by control system,the ~ 2.6MHz can be obtained.In particular,in order to further study the relationship between IF signal and power,the long time record of IF signal is carried out,and the intermediate frequency signal can be stabilized for a few minutes in the range of 2MHz to 3MHz.At the same time,in order to verify the theory of intermediate frequency,the resonant cavity length is adjusted to accurately analyze the change of IF signal.In the experiment,the basic relation of the intermediate frequency signal is gradually increased and the power is gradually reduced through the resonant cavity is continuously adjusted.The fluctuation of beat signal is analyzed and the corresponding reasonable interpretation results are given.The reconstruction design of the optical path greatly improves the discharge efficiency of the device.The improvement of the resonator adjustment mechanism enables the control precision to be improved,and the upgrade of the rotating grating can be applied in the future optical system to improve the time resolution of the interferometer.The results of this study show that the two color laser system has been successfully established,and the output characteristics of the IF signal is analyzed,which lays a foundation for t he precise control of the intermediate frequency and has a certain engineering value.