Study On The Characteristics Of Magnetization Field Induced By Tight Focus Of High-order Laguerre Gaussian Beams

In recent years,the tight focus of the unevenly polarized vector beam has received great attention.By changing the spatial distribution of the polarization of the incident light,some interesting phenomena are generated.For example,the radially polarized light will produce a purely longitudinally distributed electric field under tightly focused conditions;the angularly polarized light will be strong under tight focus conditions.Longitudinal magnetic field.was widely used in ultra-high density magnetic storage,magnetic particle manipulation,nanolithography,particle sub-acceleration and other fields.Based on the Richards-wolf diffraction theory and the inverse Faraday effect,the high-order LG beam is modulated by a special phase filter.The effects of optical parameters such as polarization,amplitude and phase distribution of the incident light on the induced magnetization field characteristics are studied.The main research contents are as follows:Based on the inverse Faraday effect,the magnetization field characteristics induced by the high-order radial polarization Laguerre Gaussian(LG)beam at the focal plane are studied,and the radius of the incident light is studied with the cutoff parameter(?).By adjusting the value of the cutoff parameter,a bottle-shaped hollow magnetization field structure and a hollow dark channel along the optical axis direction can be obtained.The distribution of magnetization field is calculated by Matlab simulation,and the five-loop phase filter is optimized,and the physical mechanism of forming ultra-long symmetric magnetic needle is clarified.The three-dimensional super-resolution magnetic spot generated by the high-order radial vortex LG beam under the 4? focusing system is studied.Firstly,the focused light field at the focal plane of the single lens and the induced magnetization field are calculated,and the light field components affecting the distribution of the magnetization field are analyzed.The 4? focusing system is used to modulate the incident light to enhance the longitudinal component of the focus field,thereby effectively reducing the magnetic spot size.In order to achieve a super-resolution distribution of the magnetic field over a larger range,side lobes due to increased topological charge are reduced.We use a three-loop phase filter to modulate the high-order radial vortex LG beam to obtain a three-dimensional super-resolution spherical magnetic spot with a relatively uniform distribution over a larger range.At the same time,in order to study the application of the generated magnetic particle in manipulating the particle,the distribution of the magnetic field force was simulated by Matlab,and the equilibrium position of the magneticparticle in the magnetic spot was obtained.Further,the magnetic particles are effectively controlled.The high-order mixed-polarized LG beam induces the distribution of symmetrical magnetization field in the focal plane.The effects of different topological charge,amplitude and truncation parameters on the magnetization field characteristics induced by the tight focus of high-order mixed-polarized LG beams are analyzed.In order to produce the ideal magnetic spot distribution,the influence of numerical aperture on the size and position of the magnetic spot was studied.Through the regulation of the beam parameters,the number of control magnetic spots and the position of the magnetic spots are optimized to achieve the purpose of capturing more magnetic particles.