Research On New Laser Radar System And Its Laser Source

In recent years,three-dimensional imaging lidar has been one of the hot spots in remote detection.Compared with traditional microwave radar,lidar with fine time and spatial resolution can be used for precise range measurement and imaging.So in the military and civilian fields it has broad application prospects.This paper mainly focuses on the design and implementation of imaging laser radar with different methods.Three parts of work were mainly included.Firstly,a three-dimensional imaging lidar Based on Compression Sensing was experimentally studied.Secondly,a new ultra-long distance lidar scheme based on frequency locking technology and photon detector was proposed and we developed a laser based on PDH frequency locking technology.Thirdly,a high power ultrashort pulse mode-locked fiber laser with potential application of LIDAR was experimentally studied.Compressive sensing is an emerging theory about signal sampling and recovering.It has become a research hotspot because of breaking the classic Nyquist-Shannon sampling theorem to a certain extent.The theory points out that when the target signal is sparse,the target signal can be reconstructed with the number of sampling times much lower than what the classical sampling theorem requires.The first part of this thesis introduces the basic principle of compressive sensing theory and the new three-dimensional lidar based on this principle which was designed by our group.Imaging experiments were performed on a 50-meter target and a 220-meter target using the lidar.The horizontal spatial resolution of the system was experimentally tested,and the result has proved that the lidar based on compressive sensing theory has great potential for high resolution imaging with low sampling times.In the second part of this thesis,a new type of lidar scheme based on laser frequency-locking technology is proposed.The radar scheme uses PDH frequency locking technology to lock a single frequency laser to a resonant frequency of the FP cavity.Additionally,a photon detector with a much higher sensitivity than the photomultiplier tube is used as the detector in the scheme.The incident light of the photon detector is filtered by the same FP cavity which has been used in the PDH laser.Compared with existing lidars,the new type of lidar can achieve more distant target detection theoretically.In order to verify the feasibility of this program,a laser which could be frequency locked dynamically was constructed with a DBR laser and a space FP cavity by using the PDH frequency locking technology.At the same time,a novel ultra-narrowband optical filter was designed based on the FP cavity and the interference filter.We tested the filter combined with the photon detector.It was found that the new filter can effectively filter the clutter interference from the background.These experiments validate the feasibility of this scenario.In the third part of this thesis,we studied the high power mode-locked fiber lasers that can output ultrashort pulses.Since the wide spectrum of the laser,if you use FP cavity filter,you can get a bundle of several wavelengths and the same frequency interval of ultra-short pulse laser,in the field of laser radar has great potential value.In this part,a mode-locked laser is designed based on the nonlinear polarization rotation technique,and the power is amplified by the MOPA technology.A pair of gratings was introduced before the main power amplifier to adjust the initial pulse dispersion.Finally,the laser output pulses with the average power of 12W and the pulse width is less than 100fs.