Research On Generation Of High Power Radially Polarized Beams Based On Vector Polarization Resonators

The rotational symmetry of the polarization distribution of radially polarized beams makes it unique in laser processing,optical microscopy,particle capture,plasmon polaritons,and laser acceleration applications.In this paper,theoretical and experimental studies on the generation of high power radial polarized light based on vector-polarized resonators are carried out.The main research content is as follows:（1）The numerical calculation theory of vector polarization optics is studied,including the matrix theory of polarization optics（Jones vector,Jones matrix,Stokes parameter,Miller matrix,etc.）,characterization of vectorial polarized beam,and diffraction integral theory of vector field,which lay a theoretical foundation for the numerical calculation of polarization optics and polarization-sensitive resonators.（2）The calculation method of the eigenmode of the polarization-sensitive resonator is studied.Based on the Jones vector theory,vectorial Fox-Li iteration method and vector eigenvector method（VEM）for the calculation of the eigenmodes of a polarization-sensitive resonator are proposed.Compared to the vector Fox-Li iterative method,the VEM can solve multiple eigenmodes in a polarization-sensitive cavity at a time,including scalar mode and vector mode.（3）The mode characteristics of a spherically polarized vector resonator are studied.The effects of polarization parameters,Fresnel numbers,and geometric parameters of the spherically polarized vector resonator on the mode selection and mode field distribution in the cavity were investigated using the VEM.It is concluded that in order to obtain the minimum order vector polarization mode in a spherically vectorially polarized semi-confocal cavity,the difference between the TM and TE polarization reflection coefficient of the polarization device should be greater than 0.0225 and the Fresnel number of the cavity is in the range of 2 to 2.5.Then,a vector-polarization-converted resonantor was designed to achieve the conversion of the angular polarization and radial polarization,andthe output of radial polarized light of 2000W was achieved based on the fast axial flow CO₂ laser platform.（4）The mode characteristics of the toroidal vector-polarized resonator are studied.The inhibition effect of common toroidal resonators on the competitive modes such as TEM00mode is studied.Then,the effects of the polarization parameters,Fresnel number and geometric parameters of the toroidal vector polarized cavity on the mode selection and mode field distribution in the cavity are studied.It is concluded that for the toroidal vector-polarized semi-confocal cavity,that the difference between the TM and TE polarization reflection coefficient of the polarization device is greater than 0.0160 and the Fresnel number of the cavity is in the range of 4 to 5.5 are required.Besides,the toroidal-polarized resonant cavity helps to obtain a vector-polarization mode compared to a spherically-polarized vector resonant cavity.（5）The misalignment characteristics and thermal stability of spherical and toroidal vector polarized resonators are studied.The tilt and off-axis misalignments of spherical and toroidal vector-polarized resonators are analyzed using the augmented matrix analysis method and the equivalent optical path misadjustment factor method.Both the tilt and off-axis misalignment can cause eccentricity and depolarization of the mode field.The misalignment sensitivity of the toroidal vector polarized cavity is greater than that of the spherical vector polarized cavity.Then,using the finite element analysis method,the thermal deformation effect of the axicon was studied.In the high-power operating environment,the deformation of the axicon is larger than the wavelength,which has a certain influence on the radial polarization mode and laser efficiency of the laser.Therefore,it is necessary to enhance the cooling effect.