Theoretical Model Of Strain Sensing Method And Spectral-image Analyzing Technology Based On Second Harmonic Generation

In recent years,the nonlinear optical effect of two-dimensional materials under ultra-short laser has attracted more and more attention with the development of laser and micro/nano technique.As a typical nonlinear optical phenomenon,second harmonic generation(SHG)gradually becomes a hot-point in the fields of optics and spectrology.According to the existing studies,the nonlinear optical susceptibility can be affected by strain,ultimately leading to the change of SHG intensity.Especially,two-dimensional materials such as molybdenum disulfide(Mo S₂)have advantages of stable SHG and high sensitivity to strain,and lager affordability of external strain.Therefore,this work provided a new method of strain sensor based on SHG of Mo S₂ by conducting the basic investigation on its experimental theoretical model and spectral-image analysis technology.First,the polarization-intensity formulas were derived under strain-free and different strain states according to theoretical model of SHG for Mo S₂.The evolution and regularity of polarization-intensity spectra induced by strain were detailedly analyzed and systematically described.Then,the theoretical model of the strain sensor was established with Mo S₂ as the sensing medium and the polarization-intensity formula under arbitrary strain state was deduced.Using the information detected from the polarization-intensity spectra,the analytic and fitting methods were proposed to calculate the strain components.Based on the fitting method,the technique of the spectral-image analysis was proposed,as well as the processing flow and calculation program.Taking the thin plate with a circular hole under uniaxial loading as an example,a numerical experiment was carried out to verify the correctness and applicability of the technique of the spectral-image analysis.Besides,the microscopic device of SHG strain sensor was developed.The coaxial optical path was designed and some key components were selected and analyzed,realizing the establishment of the optical system.In sum,this stablished the foundation for the application research full-field strain-sensing sensing at the microscale using Mo S₂ as the sensing medium by proposing the theoretical model,developing spectro-image analysis technique,and constructing the optical system.