Study On The Generation Of Special Correlated Partially Coherent Beams And Its Propagation And Focusing Properties

With the wide application of laser in industrial,agricultural,medical,military and other fields,new beam models have been proposed and generated experimentally,which greatly enriches the types of laser beams.It is found that the special correlated partially coherent beams generated by adjusting the coherent correlation structure of the optical field have unique propagation characteristics such as self-splitting,self-focusing,self-drift and self-shaping,which can effectively reduce the influence of atmospheric turbulence on beam propagation properties.The special correlated partially coherent beam after focusing is accompanied by the transfer of energy and momentum when it interacts with matter,which is widely used in manipulation,capture,screening particles and so on.The establishment of a new special correlated partially coherent beam model,experimental generation and control,propagation and focusing,and capture characteristics are studied.The main work and innovations of the thesis are as follows :1.Based on the basic theory of partially coherent beams,four models of partially coherent quasi-rectangular correlated Schell-model beams,superimposed Hermite-Gaussian correlated Schell-model beams,off-axis multi-vortex superimposed Hermite-Gaussian correlated Schell-model beams and off-axis multi-vortex partially coherent crescent-like correlated Schell-model beams are proposed.2.Based on the generalized Huygens-Fresnel principle,the expressions of beam intensity,root-mean-square beam width and beam drift of partially coherent quasi-rectangular correlated Schell-model beams in non-Kolmogorov spectrum are derived.The evolution of the off-axis distance of the peak intensity position with beam parameters and turbulence parameters is analyzed.In atmospheric turbulence,the root-mean-square beam width of such beams increases with the increase of refractive index structure constant,the outer scale of turbulence or the decrease of the inner scale of turbulence.There is a large beam drift in the case of large initial waist width,large turbulent outer scale or short wavelength.When the initial beam width and coherence length are small,it is beneficial to the long-distance propagation of the beam.3.Based on the second-order moment theory,the expressions of beam intensity,propagation quality factor,root-mean-square beam width and beam drift of superimposed Hermite-Gaussian correlated Schell-model beams propagating in non-Kolmogorov spectrum are derived.It is found that the beam has both self-splitting characteristics and annular intensity distribution characteristics.Compared with the Hermite-Gaussian correlated Schell-model beam,the superimposed beam has faster self-splitting speed and lower propagation quality factor,which can effectively reduce the influence of turbulence on the beam propagation quality.Based on the Rayleigh scattering theory,the scattering force and gradient force of the off-axis multi-vortex superimposed Hermite-Gaussian correlated Schell-model beam on the particles after focusing are calculated.The results show that the beam can achieve multi-point capture of multiple particles.4.The superimposed Hermite-Gaussian correlated Schell-model beam,off-axis multi-vortex superimposed Hermite-Gaussian correlated Schell-model beam and off-axis multi-vortex partially coherent crescent-like correlated Schell-model beam are experimentally generated,which verifies the correctness of the above theoretical model.By adjusting the parameters such as the number of vortices,the off-axis distance of vortices,the initial phase angle of vortex position and the number of topological charges,the off-axis multi-vortex beams will carry a number of vortex singularities with different hollow degrees at different positions.The multi-vortex makes the energy flow on the cross section present a spiral distribution,and changing the off-axis distance of the vortex can realize the flexible adjustment of the peak position of the light intensity.