Study On Propagation And Scattering Of Non-diffraction Beam In Medium

Great interest has arisen in the study of non-diffraction beam for its special properties of non-diffraction and self-construction.It has been widely used in various fields,such us precision optical detection,optical acceleration,optical manipulation and optical confinement.Deep understandings of interaction between non-diffraction beam and various kinds of medium will certainly be helpful of steering the beam for better performance.Firstly,the propagation of on-axis and off-axis Bessel beam in a gradient-index medium is studied.By expressing a Bessel beam in integral form,the analytical expression of an on-axis,decentered,and tilted Bessel beam through a paraxial optical system is derived with the ABCD matrix method and Collins diffraction integral formula.Main lobe size and trajectory of the zeroth-and second-order Bessel beam are obtained,demonstrating that the Bessel beam is focused by the gradient-index medium and its main lobe trajectory is exactly the same as the corresponding geometrical ray for both the decentered and tilted Bessel beam.Effects of beam apodization are finally studied by the Fourier beam propagation method,showing that the side lobes of the Bessel beam vanish when the beam is focused inside the medium as only part of the beam enters the lens.The study will be helpful to get a deep understanding of shaping Bessel beam with a gradient-index lens.Secondly,the propagation characteristics of Bessel-Gaussian beam in a gradient-index medium is investigated.The propagation trajectory,intensity,and phase distributions of the zeroth-order,second-order,and superposition cases are numerically investigated.The effect of beam waist radius on the properties of beam propagation in a gradient-index medium is discussed in detail.The result shows that the beam is focused at z?L = N?2(N = 0,1,2,…)and propagates periodically in the medium.Evolution of the vortical structure of the superposed Bessel-Gaussian beam is investigated,showing that the superposed beam forms new singularities,and the rotation of the beam occurs mainly near the singularities.Then,the propagation characteristics of Bessel-Gaussian beam in a chiral medium are studied.The influences of beam waist radius and chiral parameters on the propagation are simulated.The transverse intensity and phase distribution of the superposed beam at different propagation distances are discussed.The results show that the Bessel-Gaussian beam split into the left circularly polarized beam and the circularly polarized beam with different propagation trajectories.And the propagation trajectory of the Bessel-Gaussian beam in a chiral medium can be controlled by varying the chiral parameter.The results will be much helpful to understand the interaction mechanism between the structured light beams and chiral medium.Finally,the angular scattering of a one-dimensional Airy beam light sheet by a chiral sphere is numerically studied in this paper based on Mie theory and a plane-wave spectrum method.The effects of sphere radius,chiral parameters,and beam width on angular distribution of scattering light are simulated.The results show that the oscillation of the distribution curve is more obvious with the increase of chiral parameter,and the radius of the chiral sphere can be determined by the extreme value and position of the curve.