Research On The Generation And Mode Symmetry Of Vortex Light In Off-Axis Pumped Solid-State Lasers

Vortex beams have been one of the most popular studies due to their special properties of light field.In recent years,with the deepening of the researches on vortex beams,some vortex beams with special light field structures have attracted people’s attention,such as vortex beams with asymmetrical structure of intensity distribution,which have shown great development potential in the fields of optical communication and particle manipulation.Using astigmatic mode converter to convert Hermite-Gaussian（HG）beams is a common method for generating the vortex beams,which has the advantages of simple operation and high mode quality.Based on this method,this paper starts from the aspect of changing the intracavity loss of an off-axis pumped Nd:YVO₄ laser with adjustable output reflectivities and an extra-cavity single-cylindrical lens,so as to explore the method of generation of high-power asymmetrical Laguerre-Gaussian（LG）beams.The main contents of this thesis include the following three parts:The domestic and foreign research status and application prospect of vortex beams are briefly introduced.Several common preparation methods of vortex beams are introduced,and the advantages and disadvantages of each method are compared.Then,the conversions of HG beams into LG beams by using astigmatic mode converter are theoretically analyzed through the mode conversion theory.Secondly,an off-axis pumped Nd:YVO4 laser that can adjust the symmetry of the output transverse mode is proposed,and the output model of intracavity HG mode and LG mode is constructed,and the influence of intracavity loss on the symmetry of transverse mode output mode is explored.An image processing method to calculate the symmetry of the output spot image is proposed in order to numerically calculate the symmetry of the output laser mode in the experiment.The experimental results show that with the gradual decrease of the reflectivity of the output mirror,the asymmetry of the output transverse mode will gradually increase.And under the specific reflectivity of the output mirror,a stable output of high-power asymmetric transverse mode can be obtained.Thirdly,the experimental system of an off-axis pumped Nd:YVO₄ laser with an extra-cavity single-cylindrical lens was designed and established.The conversion process of HG beams and LG beams was theoretically and experimentally analyzed by using a single-cylinder outside the cavity.The experimental results show that as the angle between the single-cylindrical lens axis and the horizontal direction changes from 0 to 45°,the HG modes convert to the LG modes with the continuously increasing ellipticities,and then inversely convert back to the HG modes at 90°.As the output mirror reflectivities decrease from 95%to 81%,and 60%,the LG modes symmetries of 93.5%,71%,and 40%,are realized,respectively,which are consistent with the numerical simulation results.When the output mirror reflectivity is 60%,the output powers of the asymmetrical LG modes with different radial indices exceed 1 W with a pump power of 6.36 W.