| Lidar is an optical remote sensing technique to detect target properties by analyzingtarget’s reflected or scattered echo signals. The information obtained from the echo signalinclude light’s intensity, frequency, phase, polarization, target distance, and so on. As therapid development of laser technology, the application of advanced signal detection anddata acquisition technique, lidar has been used in many areas with the advantages of highspatial and temporal resolutions, large detecting range, fast measurement speed andabundant information.The main research works of the paper are the key opto-mechanical technology for lidarweak signal detection. The paper can be divided into two parts. One is detecting globalwind from space platforms, the optical parameters of coherent wind lidar system at400kmorbit are optimized based on the derived SNR formula, furthermore, the opto-mechanicaldesigns are presented. The other part is laser-induced fluorescence lidar system, in which aICCD-based system with leading comprehensive technical indicators at home and abroadwas introduced, the main responsibility in this program is to develop a fluorescencespectrometer whose spectral range is290nm-650nm and spectral resolution is2nm, solvingproblems such as elastic scattering is too strong under dual-wavelength detection mode andspectra with different diffracted order located at the same position.The main innovative work of the paper are described as follows.1)The detection mode which employing two telescopes was introduced, avoiding theproblems such as expensive and high-power-using scanning optical wedge if singletelescope is used. The expressions of system efficiency, heterodyne efficiency, SNR andother important indicators are deduced and calculated using back-propagated localoscillator(BPLO) approach based on the Gaussian model, the optical parameters such as thetelescope aperture, the divergence angle and truncation ratio are derived.2) In space-based coherent wind lidar system, single-mode fiber is used in the systemdesign to deliver local oscillator laser and the signals collected by the telescope.With thereason that it is difficult to keep high alignment requirement for free-space optical systemin several years and almost impossible to do maintenance operations for spacebasedplatforms, single-mode fiber is used in the system design to deliver local oscillator laserand the signals collected by the telescope. The theories of coherent wind lidar based on free space and optical fiber are combined with a similar form, then the F#(The ratio betweenfocal length and aperture) of coupling lens is optimized. In addition, a lag anglecompensator was designed for the spacebased coherent wind lidar system.3)According to the optimized optical parameters, the off-axis telescope with500mmaperture was designed for400km orbit and the tolerance requirements was presented under1/10λ@2μm wavefront error, besides, the designs of coupling lens and the beam expanderare also introduced. Furthermore, a lightweight mechanical design was described andsystem characteristic parameters such as volume, weight, overall system efficiency weresimulated.4)With considerations of fluorescence characteristics such as short lifetime, lowintensity and wavelength sensitivity, a detection strategy based on time-gated ICCD wasproposed. In order to obtain more fluorescence information dual excitation wavelengthslaser (266nm and355nm) was investigated, and a fluorescence spectrometer was developedaccording to specific ICCD shape and spectral band (290nm-650nm), such fluorescencespectrometer can also eliminate the elastically scattered light. According to the test results,the center-resolution and edge-resolution of fluorescence spectrometer can reach1.6nm and2.5nm, which is better than most of the same type of fluorescence spectrometers used inexisting fluorescence lidars, finally, several oil fluorescence spectra were collected andprocessed with the laser-induced fluorescence lidar. |
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