Research On Theory And Critical Technologies For Water Brillouin Scattering Detection Using Double Edge Method

The temperature and salinity of sea play critical roles in the physical,chemical and biological processes.Therefore,obtaining temperature salinity through remote sensing methods receives constant interest from researchers.Among all the remote sensing methods,laser have a unique advantage of obtaining vertical distribution of water physical parameters due to its lower attenuation in water.The Brillouin scattering carries information closely related to water physical parameters in its spectral lineshape,and has narrow spectral band and relatively strong scattering intensity,which make it possible to collect strong,background noise-insensitive signal.Therefore,Brillouin scattering has strong potential in the remote detection of water temperature and salinity parameters.However,existing detection methods of water Brillouin scattering cannot achieve real-time measurement,continuous measurement,and complete measurement of Brillouin spectrum at the same time.To meet those requirements simultaneously,this dissertation propose a method of measuring Brillouin scattering spectrum with double edge detection and conducted theoretical and experiment research on this method.On theoretical aspect,this dissertation construct retrieval model to obtain Brillouin shift and linewidth using transmission energy of to edge filters.Then conduct parameter optimization for edge filters,analyze uncertainty of Brillouin shift and linewidth retrieval result and finally calculate uncertainty of temperature and salinity measurement.Under 1% uncertainty of edge transmitted energy,the uncertainty of frequency shift and linewidth are 3MHz and 6MHz respectively,which correspond to0.5? water temperature uncertainty and 1.2‰ salinity uncertainty.Those theoretical work prove the viability of double edge method in the profiling of water Brillouin scattering.On experimental aspect,this dissertation discussed the following topics:Frequency locking and frequency shifting module of laser source,Iodine absorption cell for laser frequency locking and noise suppression,Double channel Fabry-Perot etalon used for edge filtering.For laser frequency locking and frequency shifting modules,this dissertation participated in design and implementation of frequency locking system based on linear absorption of iodine cell and frequency shifting system based on optical phase locking.With respect to iodine cell,absorption spectrum is studied through simulation and experimental measurement to select suitable absorption line for this project.Simulation is also conducted to evaluate suppression effect of Rayleigh-Mie scattering with iodine gas cell.Under testing condition,the energy ratio of Rayleigh residual :single side Brillouin energy is 106.5% in the iodine filtered signal.For Fabry-Perot etalon,theoretical evaluation is conducted to analyze its thermal stability,thermal and angular tunability and transmission broadening caused by beam divergence.Experimental evaluation is conducted to determine spectrum parameter,working temperature and thermal drifting effect of the etalon.Under the working temperature of 55?,the two channel of have FWHM(Full width at half maximum)of287.00 MHz and 289.31 MHz respectively,with frequency separation of 4.038 GHz.The effective finesse of etalon is higher than designed value and satisfy the requirement for system implementation.This dissertation builds theoretical model for double edge method in water Brillouin spectrum detection and perform design,analyze and test of critical system modules.Those work lays theoretical foundation and partial experiment foundation for the construct of a complete experiment platform.