Study Of Multi-channel Photoelectric System For Absolute Detection Raman Temperature Lidar

Atmospheric temperature profile is of great significance for the atmosphere transmission and radiation,meteorology change,atmosphere radiation balance,etc.The rotational Raman lidar,as a new remote sensing tool for atmospheric temperature,give helps to atmospheric science research,fine weather forecast and early warning and forecast services of special meteorological events.However the existing Raman lidars need parameter calibration because of their retrieval method dependence on two opposite temperature sensitivity rotational Raman signals,whereas the atmospheric temperature profile can be accurately retrieved without calibration by the multi-channel Raman lidar,which is of significance for the application of atmospheric temperature detection lidar.Aimed at the absolute detection of atmospheric temperature,absolute detection temperature technique is studied based on multiple nitrogen rotational Raman spectra,according to Raman scattering theory.A two-stage multi-channel Raman spectroscopic system is optimized by using blazed grating and fiber Bragg grating.The line spacing between anti-stokes Raman with even quantum number of nitrogen molecules match the fiber cladding diameter,considering the influence of the oxygen molecule spectra,and then six lines(J=2,4,6,10,12,16)are chosen for the retrieval of atmospheric temperature profile.Fiber array is designed to extract spectral lines,and then its quality factors are discussed.The coupling efficiency is also analyzed based on mode coupling theory.We discuss the dependence of coupling efficiency on the lens diameter and the single-mode fiber mode field radius.The coupling efficiency can reach 0.812,as the coupling lens diameter of 50 mm,focal length of 220 mm,and single mode fiber mode field radius of 1.75?m.Since there exists deviation between actual processing fiber array and ideal optical fiber array,we build the coupling model and analyze the coupling efficiency influence of bias such as lateral offset,vertical offset and deflection angle.The simulation results show that the system coupling efficiency can reach above 0.45,as optical fiber core spacing deviation within 1?m,the defocusing amount of coupling lens within 20?m.Furthermore,a photoelectric detection system is built with multi-channel photomultiplier tube.The experimental results show that the gain consistency can reach over 92%among channels,and that the channel crosstalk is less than 0.2%.Multi-channel spectrometer system made up of blazed grating and fiber Bragg grating is assessed by using wide spectrum light source as the optical source.The experimental results show that the center wavelength of each channel has maximum bias of 0.03 nm to simulation result,which is generated by the fiber core spacing offset.Theoretical research and preliminary experimental results show that the multi-channel photoelectric detection system has good gain uniformity and low crosstalk,and that the center wavelength has high consistency to the simulation results.It may provide a reliable technical support to build multi-channel Raman lidar and promote the practical application of Raman temperature lidar.