| Light field control is widely used in optical communication,light field structure changes,laser beam transformation and other fields.With the increasing demand for different light field structures,a single light field structure can not meet the needs of different fields,so the research on light field control becomes more and more meaningful.The research content of this paper mainly includes the generation of long focal depth vector beam and single focus optical vortex.On the one hand,optical elements with long focal depths and high lateral resolution are of great significance in material processing,optical guiding of microscopic particles and formation of plasma waveguides.At present,a variety of methods have been proposed to generate light field with long focal depth,including axicons,refractive-diffractive hybrid element and computer-generated hologram.The mirror proposed in this paper can be used for producing centimeter focal depth with high intensity,which plays an important role in the fields of Thomson scattering,charged particle acceleration and other fields.On the other hand,the vortex beam with helical phase wavefront structure is also an important part of light field control.Due to its special orbital angular momentum degrees of freedom,vortex beams have a wide range of applications in particle manipulation,optical communication and other fields.In this paper,the optical vortex with single-focus characteristics can be obtained by modulating the incident plane wave based on two new spiral zone plates.The main content of this paper is to study the tight focusing characteristics of long focal depth mirror with special curved surface structure and the diffraction characteristics of two kinds of helical zone plates with single-focus characteristics.The main work is summarized as follows:1.Firstly,the research background and significance of light field control are introduced.Secondly,for the long focal depth light field and optical vortex,the generation methods and applications of two different beams are introduced.Then the scalar and vector diffraction theories are introduced in detail,which is the theoretical support of numerical simulation in this paper.Finally,the design principle and tight focusing characteristics of the mirror and the design principle,focusing characteristics and experimental verification of the single focus spiral zone plates are introduced.2.Based on the principle of energy conservation and equal optical path,combined with aspheric equation,a new type of large numerical aperture mirror is proposed.Numerical simulation is carried out based on Richards-wolf vector integral,and the tight focusing characteristics of the novel mirror are studied in detail.The mirror presented in this paper can be used to focus high-power ultrashort pulse laser with pulse width of picoseconds or femtoseconds,and there are many potential applications in physics of strong field.3.In order to obtain a single-order focused vortex beam,we propose the quasi-random-dot-array binary spiral zone plates composed of seamless and closely laid primitives.The number density of primitives is sinusoidal and quasi random along the radial and latitudinal directions respectively.Based on the scalar diffraction theory,the characteristics of restraining high-order focusing are verified by numerical simulation,and the experimental results also verify the accuracy of the simulation results.The novel element provides a new way to improve biomedical imaging and quantum computing.4.Binary single focused square spiral zone plates can produce optical vortices with square symmetry.The key idea is to realize the sinusoidal transmittance along the radial direction to suppress the interference of high-order harmonics.Based on the scalar diffraction theory,the focusing characteristics are studied and verified by experiments.The element with unique square structure has important application value in alignment system. |
