Controllable Laser Output Of High-quality Spatial Light Through Intracavity Mode Conversion

In recent years,intrigued by the applications of laser technology,many new spatial light fields such as vortex beam,vector beam,and Bessel beam have been realized experimentally.The unique properties of these spatial light fields enable them to be applied in particle manipulation,quantum communication,quantum computing,information transmission,super-resolution imaging,edge enhancement imaging,three-dimensional modulation of light,and so on.The spatial structured light is normally generated by q-plate,fork grating,and spatial light modulator,as well as putting etalon,paired nanowires,or birefringence crystal in a cavity.However,the existing methods cannot fully meet the needs of generating high-quality spatial structure beams.Based on the mode conversion in laser cavity,the laser output of controllable,high-efficiency,high-purity and high-order spatial structure beam(including Laguerre-Gaussian beam and cylindrical vector beam)is realized in this paper.The details are listed as follows:1.We construct a 1064nm.solid-state laser which can produce LG10 and LG20 beam,and l = 1 and l = 2 cylindrical vector beam.We adopt the end-pumped 1064nm continuous laser cavity,where a plane mirror,a concave mirror and a plane mirror form the resonant cavity to precisely control the spot size.When generating a Laguerre-Gaussian beam,a vortex half-wave plate is used for the intracavity mode conversion,and the Faraday rotator,1/4 wave plate,and polarization beam splitter are used to achieve cavity mode reversibility.When generating a cylindrical vector beam,the whole process is reversible by using a vortex half-wave plate and a polarized beam splitter.2.We have measured the purity of Laguerre-Gaussian beam and the polarization purity of cylindrical vector beam.When measuring the mode purity,the phase image carrying the information of Laguerre-Gaussian eigenmode is loaded on the spatial light modulator,and we obtain the modal decomposition results in the focal plane.When measuring the polarization purity,a 1/2 waveplate,a 1/4 waveplate and polarization beam splitter is used to obtain the horizontal,vertical,angular and anti-angular,left-handed and right-handed circular polarization components.The polarization purity is solved based on Stokes parameters.3.The laser parameters,including the curve of output powers,spot shape at different power,beam quality factor,mode purity,polarization purity,and so on,have been measured.The experimental results verify the high-quality laser output of spatial structured light.