Research On Fiber Photo-thermal Interferometry For Absorption Properties Measurement Of Atmospheric Aerosol

Atmospheric aerosol particles absorption plays an important role in earth atmospheric radiation balance and laser atmospheric propagation,although the value of absorption coefficient is small.Now,the research of atmospheric aerosol particles absorption coefficient measurement attracts more and more attentions,and becomes one research hotpot and technical difficulty.Compared with the traditional method,the photo-thermal interferometry(PTI)can directly measure the aerosol particles absorption under the nature suspension status.In substance,this method detects the refractive index induced by aerosol absorption thermal diffusion effect.So the influence of scattering light can be neglected.On the other hand,the interferometry has very high detection sensitivity.Therefore,the PTI is considered to be a promising method for atmospheric aerosol particles absorption coefficient measurement.In the present work,the research on fiber photo-thermal interferometry for absorption properties measurement of atmospheric aerosol has been done.The measurement principle of PTI has been elucidated.The fiber Feazu photo-thermal interferometer structure which adapted to the atmospheric aerosol absorption coefficient measurement is designed.A preliminary study of the aerosol absorption character has been done.The main merits and innovations of this thesis are as follows:(1)The whole transfer progress of the photo-thermal-refractive-phase has been derived from the thermal conduct equation,based on the photo-thermal effect of aerosol particles absorption.A direct link is established between the atmospheric aerosol absorption coefficient and the interferometry output phase signal.(2)The synchronous carrier restoration(SCR)method has been present which can eliminate the phase difference between the carrier mixing signals and the interference signal and effectively mitigate the phase delay effect.The problem of the amplitude modulation induced by directly current modulation is solved by the reference optical path method.The demodulation and control software of PTI based on the phase generated carrier(PGC)algorithms is completed which can effectively resolve the phase shading phenomenon of interferometry,restore and present the whole process of phase fluctuation induced by aerosol particles light absorption,synchronously.(3)Designed and established a fiber photo-thermal interferometry experimental instrument for aerosol absorption measurement.With the custom-made fiber collimator and reflector,the common-path fiber Feazu interferometer structure has been realized,which can resolve the couple difficult of the photo-thermal and the phenomenon of polarization fading.With the integrated photo-thermal cavity design,the stability and efficient of the system have been improved.(4)The principle of calibration of the system has been elucidated,and the calibration experiment has been done with the standard Nitrogen dioxide.The measurement of the carbon aerosol has been done,and the experiment results are according well with the theory prediction which lays the foundation for further study of aerosol absorption measurement.