Characterization Of Laser Propagation In Metal/Dielectric Coated Hollow Waveguides

Hollow waveguide(HWG)is regarded as a promising device for infrared(IR)laser transmission.With the significant advantages of high power threshold,low transmission loss,broadband transmission and flexibility,HWG has been applied in various fields ranging from environmental monitoring to medical diagnosis and industry.Precise characteristic parameters of laser transmission are required in the design of HWG application systems.In order to meet the needs of the current application,it is necessary to study the laser transmission characteristics of the AgI/Ag coated HWG.The main works are summarized as follow:Firstly,a membership function for optical observations evaluation and a membership-function-weighted nonlinear fitting algorithm(MFW-LM)was proposed.Taking the idea of fuzzy logic,we devised a membership function for optical sensing data to evaluate the observations' fidelity.The proposed membership function was further used as a weighting function for signal modeling and reconstruction under expected mathematical model constraints,namely the MFW-LM algorithm,which greatly reduced the excessive influence of outliers and distortion data in the small dataset on the fitting process and simplified the steps of data processing.The robustness and effectiveness of the MFW-LM algorithm were demonstrated by an optical sensing simulation and its application in laser-absorption spectroscopy and laser-beam profile reconstruction.Secondly,the multi-position measurement of the laser-beam profile in the HWG was realized by the method of replacing the incident laser by the emitted laser.We proposed a novel method for the first time that comparing the laser-beam profiles emitted from the HWGs with different lengths and curvatures to obtain the laser transmission loss.Thereby,the laser-beam profiles at different transmission positions in the HWG were equivalently simulated.The problem that the energy and profile of the incident laser under experimental conditions are difficult to accurately measure was solved.And based on this research method,the multi-position measurement of the laser transmission characteristics in the HWG was realized.Thirdly,a new expression of the laser transmission characteristics of AgI/Ag HWG was obtained.The Lorentz-Gauss beam was incident on the AgI/Ag HWG.Through the proposed multi-position measurement method,we found that the attenuation coefficient is inversely proportional to the length of the HWG in a certain range.And an equation was established to calculate the attenuation of the transmitted laser by any length of HWG.It was fully explained by the relationship between attenuation and laser transmission angle.Compared to the averaged attenuation coefficient in the datasheet of the HWG,the proposed calculation method reduces the attenuation error by 73.6%.At the same time,the calculation method was applied to the curved HWG experiment.Based on that,the theoretical formula that the attenuation caused by bending is proportional to the curvature was verified,and the error was as low as 3.1%.In this paper,based on the proposed MWF-LM algorithm,the laser-beam profile emitted from AgI/Ag HWG was extracted,so that the laser-beam profile transmitted in the HWG was equivalently analyzed in multiple positions.A new representation between the attenuation caused by HWG and its length was obtained.And it was verified that the additional attenuation of the transmitted laser caused by bending is proportional to the curvature of HWG.The results of this paper are of great significance for the development of HWG application system design.