Research On The System Of Wind Lidar Based On Frequency Discrimination By Angle-Tuned F-P Etalon

With the rapid development of laser devices and technology, the direct detection Doppler wind lidar becomes more and more attractive in America, many European and Asian countries since the 1990s. It can use echo signal including Mie and Rayleigh backscattering to measure Doppler shift which is suitable for global wind field measurement. The stabilized injection-seeded laser and frequency discrimination system with thickness tunable F-P etalon are key devices in traditional Doppler wind lidar, but it has some shortcomings such as high price, difficulty in processing and rigorous environmental requirement. To address these problems, this dissertation proposes Doppler wind lidar based on passively Q-switched laser in twisted mode folded cavity and angle-tuned F-P etalon, and performs theoretical and experimental studies.Theoretically, 1. We have made a simulation research of differential cross section, echo power and spectral distribution of Mie backscatterting according to lidar equation of single scattering. Simulation results show that the aerosol backscattering ratios for laser operating at a wavelength of 1.064μm is 4-6 times of that with a wavelength of 532nm or 355nm which shows that 1.064μm is suitable as laser source for Mie scattering lidar. 2. Mathematic model of F-P etalon with Gauss defects is obtained by means of using the recurrence method based on the ideal transmission function of F-P etalon. We have studied the influence of incidence and divergence on the transmission curve of F-P etaton by using the model. The results indicates that the sensitivity is about 0.3%/(m/s) as the incidence increasing 2mrad for F-P etaton with a free spectral range(FSR) of 5GHz and a finesse of about 11. It is in good agreement with experimental results. 3. The mathematic model of the transmitted light power of F-P etalon is established by convolution of laser intensity with Gaussian distribution and mathematic model of F-P etalon with Gaussina defects. We have made simulation calculation of the influence of angular step of the stepping motor, defects, FWHM, aperture of F-P etalon, wind dynamic range, SNR and sensitivity on wind error. Simulation results show that the wind error is less than 1m/s by choosing the suitable parameters.Experimentally, 1. We have made research of passively Q-switched laser with single-longitudinal mode based on the grating-based frequency selection and F-P etalon in twisted mode folded cavity. Single pulse at 1.064μm with energy of 8.8mJ is achieved in TEM00 mode with a pulse width of 20ns and 10Hz repetition rate. The measured near and far field angles of divergence are 1.442mrad and 1.315mrad respectively, whose corresponding values of M2 are 1.32 and 1.31, respectively. The measured probability of single-frequency laser output is over 99% by using the methods of Fourier analysis and F-P etalon multiple-beam interferometry. The long-term frequency stability is better than 10-7. 2. Frequency discrimination system based on angle-tuned F-P etalon and a special light-dividing device has been estalished. The FSR and finesse of the F-P etalon are 5GHz and 11.48, respectively. The mechanical accuracy of angle-tuning is 36μrad. The tuning accuracy of included-angle can be increased 1-2 order of magnitude by using the special designed light-dividing device. 3. The system of laboratory velocity lidar is designed and built by using the method of angle-tuned F-P etalon. We have performed velocity measurement. The measurement results by laser are well agreed with the trend of real velocity, and the measurement sensitivity of velocity with double edges technique is 1.74 times of that with single edge technique.