Research On Mode Hopping Inhibition Of Linear Frequency Modulation Laser

In recent years,Synthetic Aperture Lidar(SAL)breaks the diffraction limit to entrance pupil diameter,improves traditional lidar spatial resolution,and becomes more and more important in coherent lidar detection system.One of the key technologies is the method of obtaining broad-band linear frequency modulation(LFM)laser.The phenomenon of mode hopping is inevasible during the laser frequency modulation process,therefore,there is a great significance for the study of mode hopping in LFM.Theoretically,the theories of laser mode and the methods of obtaining single longitudinal mode are described.By comparing the characteristics of mode selection methods,the F-P etalon method is determined as the final single longitudinal mode selection program,and the selection characteristic of various etalons with different parameter is performed.The various factors affecting the laser stability and frequency stabilization methods are described briefly.Various laser frequency modulation methods are analyzed,and the cavity length modulation method is chosen as the experimental program.From the perspective of gain and loss,mode competition is the essential reason of mode hopping in homogeneously broadened laser system,and the experimental program of mode hopping inhibition by changing angular position of the etalon and cavity length is selected.In the experimental section,the mode hopping inhibition system is designed,a control program with LabVIEW is developed,and a series of experimental analysis about LD pumped Nd:YVO4 laser frequency modulation range are accomplished.There are some experiments conducted from the perspective of changing angular position of the etalon,changing cavity length,and changing both of them coordinatively.The experimental results show that the change of etalons' angular position mainly affects the movement of free spectral range(FSR),the change of cavity length mainly affects the movement of laser mode,and only when both of them changing coordinatively can achieve the mode hopping inhibition.The frequency modulation range of 4.40 GHz is achieved,which is about twice the length of longitudinal mode interval.And the result points that the experimental system can inhibit mode hopping effectively.