Research On End-pumped Vortex Beam Laser And Propagation Properties Of Laser Beam Propagating Through Medium

The vortex beam of which each photon carries orbital angular momentum has a helical wavefront structure.The phase at the center cannot be determined,so there is a phase singularity at the center of the vortex beam,and its intensity is annular.These unique characteristics of the vortex beam make it some important applications in the fields of laser optics,atomic optics and biotechnology.At present,the generation of the vortex beam is mainly dependent on optical components,so that it has the disadvantages of high cost,low brightness,and poor beam quality.In addition,the transmission and regulation of laser beam are also an important topic in laser application research.For example,the study on the propagation characteristics of laser beam propagating through a uniaxial crystal can be used to design phase wave plates,polarizers and beam compensators,etc.The laser beam can also be used as a carrier of information,applied in the fields of atmospheric optical communication,remote sensing and target tracking.Due to the random fluctuations of the atmospheric refractive index,the beam quality of the traditional Gaussian beam propagating in atmospheric turbulence is poor.In response to these problems,this paper proposes a ring-pumped all-solid-state laser to output a vortex beam laser with high brightness and high beam quality from the resonator;Three transmission models are established,which are transmission model of flat-topped vortex hollow beam in free space and through a small opaque obstacle,transmission model of vortex beam and non-vortex beam through atmospheric turbulent,and rectangular Laguerre-Gaussian correlated Schell-model beam through atmospheric turbulence.Based on the established models,related theoretical research is carried out.The main research contents and results of the paper are as follows:1)The ring-shaped laser end-pumped Nd:YVO₄continuous output 1064nm vortex laser source is studied.When the transmittance of coupled output is 10%,the output power of 4.67W is obtained,and the slope efficiency is 43.5%.Using an acousto-optic modulator inserted in the resonant cavity,the output of the pulsed vortex laser is realized.Under the condition of repetition frequency of 1k Hz and incident pump power of 13.5w,the output single pulse energy of the vortex laser is 2.9m J and the peak power is 307.5 kw.2)The propagation characteristics between the vortex beam and the ordinary flat-topped hollow beam in the free space are compared.The results show that the intensity distribution of the vortex beam always keeps the hollow distribution in the free space.The propagation characteristics of the vortex beam passing through a small circular opaque are also studied.3)The evolution characteristics of flat-topped hollow beam,Gaussian Schell-model beam,multi Gaussian Schell-model beam and multi-Gaussian Schell-model vortex beam in uniaxial crystals are studied.It is shown that the initial coherence length and the n_o/n_e of the uniaxial crystal have a particularly important influence on the transmission of the beams.4)The beam spread and propagation factors between completely coherent beam and partially coherent beam,vortex beam and non-vortex beam in atmospheric turbulence are compared.The results show that the beam quality of partially coherent beam and vortex beam in turbulent atmosphere is better than that of completely coherent beam and non-vortex beam.The spatial coherence and propagation properties of the composited radial flat-topped vortex array beam passing through turbulence are studied.5)The rectangular Laguerre-Gaussian correlated Schell-model(RLGCSM)beam propagating through isotropic non-Kolmogorov turbulence are studied.The results show that the evolution of normalized intensity distributions of a RLGCSM beam propagating through atmospheric turbulence mainly goes through following four stages,namely,conversion from a Gaussian profile of the source plane to a flat-topped beam,self-splitting from the flat-topped beam to a(m+1)×(n+1)beam spots,then combination from the(m+1)×(n+1)beam spots to a flat-topped profile,and finally transformation from the flat-topped profile to a Gaussian profile.The RLGCSM beam with larger beam order is less affected by the turbulence and has advantages over Gaussian Schell-Model beam or Gaussian beam in turbulence for reducing the turbulence-induced degradation.