Research On The High-reflective Cavity Mirror Of Intracavity Frequency Doubling 457nm By LD-end-pumping

The 457 nm blue laser has been widely used in optical storing with high density,laser displaying,detecting seabed resource and many other fields because of its short wavelength,strong energy of photon,and full color.With the continuous improvement of the accuracy of laser application technology,higher requirement is put forward for the quality of laser beam output.As an important optical film element of 457 nm laser,the high-reflective cavity mirror plays a major role in maintaining efficient oscillation of laser in cavity,which affects the quality and efficiency of blue laser output.Therefore,it is of great significance for the research of high-reflective cavity mirror with great performance for 457nm laser.Choosing quartz as substrate material for high reflection cavity mirror,and using aspheric to improve laser intensity.In order to reduce the scattering influence on the mirror caused by surface roughness of the substrate,the preparation of the substrate was realized by using CCOS technique.According to the processing characteristics of quartz glass material,the parameters during grinding and polishing were optimized,the convergence efficiency of aspheric surface was improved by combining elastic pre-polishing for full-aperture and corrective polishing with small tool,solving the problem of high hardness and low removal rate of quartz glass material.The surface quality of aspheric was further improved by choosing polishing powder with smaller particle size and manual polishing,reducing the surface roughness.The high-reflective cavity mirror of 457nm laser has high reflectance at 457nm and fundamental frequency wavelength,and has high transmittance at wavelength of pump light and other two spectral lines with strong emission in cavity.Making H₄ and SiO₂ as high and low refractive index material correspondingly,based on the designing theory of frequency doubling reflective film,the design of high-reflective film in multi-wavelength for laser cavity surface was realized by using the software of film system designing,meeting the requirements of high transmittance and high reflectance in five wavelength,solving the difficult problem of optimization when using conventional design method.The process of evaporation with electron beam was optimized during the preparation,ion assisted deposition and staged annealing were used to improve the concentrating density and stoichiometric ratio of thin film,the spectral stability and laser-damaged threshold of the film were improved.The reason of the variation of the actual spectral curve was analyzed by inversion,ascertaining the rule of error variation.The relationship between residual thickness and film thickness was established by the method of least square fitting,which solved the problem of the spectral variation caused by the accumulation of film monitoring errors of film thickness.The reflectance of high-reflective cavity mirror prepared at 457nm and 914nm are99.9%and 99.6%,the transmittance at 808nm,1064nm and 1342nm are 97.2%,96.8%and93.1%,passed by the environmental test and laser test,which satisfies the requirements of457 nm laser.