Study On Propagation And Transformation Of Bessel Beams

The Bessel beam is a kind of special beam whose amplitude can be described by Bessel function of the first kind J0.It possess a special feature called diffractionless propagation.It was first proposed by J.Durnin in 1987.After that,people have found another unique property of the Bessel beam: self-reconstruction.These two properties make Bessel beam an attractive tool for atom manipulation,energy transmission,laser alignment and measurement,nonlinear optics,etc.The thesis is organized as follows.Firstly,the basic features of the Bessel beam,generation methods,applications and current developments are introduced.Starting from the wave equation,we discuss the foundation of the diffractionless property of the Bessel beam and introduce the common tools for analyzing the propagation properties of the Bessel beam.Then we discuss in detail the relationship among various parameters of the Bessel beam generated by an axicon based on geometric analysis.Secondly,a platform using an axicon to generate the Bessel beam is built and a method of measuring each ring size using a beam analyzer is designed to determine the beam parameters.The differences in the parameters of the beams generated by coated and uncoated axicons with the same parameters are compared.Due to fabrication errors,the actual parameters of the axicons and Bessel beam may not be in accordance with the nominal values.To solve this issue,a method is designed to calculate the actual radial wave vector of the Bessel beam using measured data.Besides,experimental phenomena are analyzed from various perspectives.Thirdly,the propagation properties of the Bessel beam after passing through obstacles of different sizes is studied theoretically based on Collins diffraction integral and then experimentally.The results indicate that if the hole is very small,the Bessel beam is no longer diffractionless but becomes a linearly expanding beam with a constant ratio of peak value between the central and outmost lobes,and that when the hole size is increased gradually,the Bessel beam evolves toward a linearly expanding beam within the geometric shadow,and the beam profile is no longer a Bessel one.In addition,the transformation properties of the Bessel beam after passing through a single lens is studied theoretically and experimentally.The results show that the Bessel beam will evolve toward a circular ring at the back focal plane of the lens after becoming a hollow beam and finally a divergent Bessel beam re-emerges under the condition that the lens is placed in the area where the Bessel beam is already formed and that the focal length is smaller than the diffractionless distance.Experiments show that this divergent Bessel beam retains the property of selfreconstruction.At last,conclusions are drawn and future work is envisioned.