Design And Realization Of The Spectroscopic System Of Fluorescence Lidar

Fluorescence lidar is mainly used to detect biological aerosol signals.It can detect particles of the size of atoms and molecules.The bioaerosols distributed in the troposphere of the atmosphere always affect our living environment.It is distributed in a wide range,such as various bacteria invisible to our naked eyes,pollen produced by plants,deadly viruses,severe smog phenomenon,decomposition products produced by animals and plants,etc.The fluorescence lidar system has the advantages of high precision and high resolution,and provides strong support for detecting the composition of biological aerosols.This thesis is mainly to design the spectroscopic system of the fluorescence lidar.At present,the light splitting devices of fluorescence laser radar are mainly dichroic mirrors and gratings.Due to the low diffraction efficiency of dichroic mirrors and low light splitting efficiency,diffraction gratings are selected as important components of the light splitting system.Reflective blazed gratings are selected because they have extremely high efficiency,wide working spectral range,large dispersion rate,and high resolution at the designed wavelength.Two schemes are adopted for designing the C-T optical splitter with a small structure folded and crossed asymmetrically and the basic C-T optical splitter.According to the spectroscopic characteristics of the grating,the number of grating lines is selected to be 6001ine/mm.According to geometric optics,two schemes are designed,and optical simulation software is used for optimization,and the spot patterns of starting wavelength(360nm),intermediate wavelength(530nm),arbitrary wavelength(640nm)and ending wavelength(700nm)can be obtained respectively.To achieve a resolution of 2nm,the two solutions meet the design requirements.The spot radius of the whole waveband of scheme one is less than 150μm,the spot radius of the whole waveband of scheme two is greater than 200μm,and the spot radius of scheme two is greater than that of scheme one,indicating that the splitting effect of scheme two is not good.Therefore,solution one is more suitable for the spectroscopic system of the fluorescence lidar.The 355nm laser was used as the excitation light source for simulation analysis,and the feasibility of the system was verified through the relationship between the atmospheric transmittance and the number of fluorescent photons and the wavelength,and the experimental conditions were met.The experimental platform of the spectroscopy system was built,and the feasibility of the spectroscopy system was preliminarily verified through a broad-spectrum light source,and the spectrum of the required wavelength band was detected.Secondly,a fluorescence lidar system was built,and bioaerosol detection was carried out by a spectrometer.At the same time,it was connected to the spectroscopic system for experimental detection.The spectrum in the 360～700nm band was detected,and the two spectrograms were compared to further verify the feasibility of the spectroscopic system sex.The detected spectrum is mixed with other noise spectrum lines,and the spectrum is decomposed by FastICA algorithm,and the mixed fluorescence spectrum,noise spectrum and Raman spectrum line are obtained.The results show that the spectroscopic system designed in this paper can detect the bioaerosol spectrum of 360～700nm,and the mixed fluorescence spectrum is decomposed from the detected spectrum through an FastICA algorithm,which will pave the way for the subsequent identification of bioaerosol components.