Controllable Laser Output Of Cylindrical Vector Beam And Laguerre-gaussian Beam Based On Intracavity Mode Conversion

With the development of laser technology,high-order laser beams including Laguerre-Gaussian(LG)beam and the cylindrical vector(CV)beam have drawn growing attentions in the past decades.LG beam has a helical phase and carries orbital angular momentum(OAM),while CV beam has cylindrical symmetric polarization distribution.These two kinds of high-order laser beams have been widely used in optical communication,particle manipulation,material processing,superresolution imaging,and precision measurement.However,the present methods to produce LG beams and CV beams still suffer from low conversion efficiency and poor mode purity.In this dissertation,based on the intracavity mode conversion thoery,we experimentally demonstrate the laser output of CV beam with high beam quality,high polarization purity,and tunable polarization distribution.We also build an optical parametric oscillator to directly and efficiently output high-purity,wavelength and topological charge tunable LG beams.The main results include:1.Controllable laser output of CV beams.The intracavity mode converter consists of a half-wave plate and a vortex half-wave plate(VWP).The cavity mode satisfies the reversible conversion from a scalar Gaussian mode to a cylindrical vector mode.The cavity parameters are optimized to achieve the designed cavity mode.By simply changing the VWP,we produce l=1 and l=2 CV beams for example.Through rotating the half-wave plate inside the cavity,the polarization distribution of the CV beams can be adjusted.For l=1 and l=2 CV beams,the polarization purity is as high as 97.8%and 96.7%,the beam quality factors M~2 are 2.1 and 3.3,and the slope efficiency is 15.5%and 5.4%,respectively.2.High-quality LG beams from the optical parametric oscillator(OPO).The Faraday rotator,quarter-wave plate,and VWP compose the intracavity mode converter.We use the Fox-Li method to design the mode distribution inside the OPO cavity,which guarantees an efficient and reversible conversion from the Gaussian mode to the LG mode.The topological charges of LG beam are tunable from-4 to 4 by altering the VWP and rotating the half-wave plate.The wavelength of LG beam from OPO is tunable from 1500 nm to 1600 nm with a conversion efficiency above 15%and a mode purity as high as 95%?...