Design And Manufacture Of Polarization-independent Multilayer Dielectric Film Grating

With the rapid development of laser technology,gratings are widely used in high-power laser systems as core components in the fields of pulse compression and spectral beam combining.The diffraction efficiency of the gratings has an important relationship with the polarization of the incident light.To improve the energy efficiency of the gratings,the multi-layer polarization-independent gratings have been studied,which have important research significance for improving the output power of the laser system and simplifying the laser system.This thesis carries out the research of high spatial frequency 1480line/mm polarization-independent multilayer dielectric film grating(MLDG),gives the design plan,and carries out the corresponding theoretical analysis and calculation.The specific work content is as follows:(1)The grating diffraction efficiency calculation is carried out based on the strict coupling wave theory,and the optimization program of grating structure design is written by MATLAB software(2)Carry out research on polarization-independent grating based on single-layer grating tooth dielectric film,construct evaluation function and use genetic algorithm to optimize grating parameters.The optimized grating structure analyzes and calculates the spectral characteristics and angular spectral characteristics.Obtained at the center wavelength of 1053nm,the single-layer grating tooth polarization-independent grating can have an average diffraction efficiency greater than 96%in the range of 30nm near the center wavelength,and an average diffraction efficiency greater than 95%in the range of ±3°near the Littrow incidence angle result.Analysis of the tolerance of the groove sidewall angle of the grating found that the single-layer grating tooth polarization-independent grating has very strict requirements for the groove sidewall angle,and it is relatively difficult to manufacture.(3)Research on polarization-independent grating based on double-layer grating tooth structure.The grating parameters are designed and optimized in the same way,and the calculated grating structure is analyzed by spectrum and angle spectrum.The results show that the theoretical value of diffraction efficiency of the double-layer multi-layer dielectric film polarization-independent grating is greater than 95.8%in the range of 50nm near the center wavelength,and the diffraction efficiency of the angular spectrum is greater than 95%in the range of ±3°near the Littrow incidence angle.Tolerance analysis of the designed grating parameters and tolerance analysis of the etching groove at the same time,it is concluded that the double-layer grating tooth structure has better process tolerance and the tolerance of the groove bottom angle,which is conducive to actual production.(4)Carry out the manufacture of polarization-independent grating with double-layer grating tooth structure.A film is coated on the glass substrate,and a photoresist mask is made by using a holographic lithography method.Finally,the groove is transferred into the SiO2 and Ta2O5 film layers by ion etching technology,and the residue is cleaned to complete the preparation of the grating.Complete the manufacture of the grating,and analyze and compare the grating pattern and diffraction efficiency.The-1st order diffraction efficiency of TE and TM waves incident at 1053nm is 96.6%and 98.0%,and the-1st order diffraction efficiency of TE and TM waves incident at 1064nm is 98.0%and 99.0%,the average diffraction efficiency in the 35nm band is greater than 96%,Consistent with theoretical analysis.