Study On The Characteristics Of The Light-induced Magnetization Field Of The Tightly Focused Vector In Uniaxial Crystals

The light-induced magnetization field is generated according to the inverse Faraday effect,which reverses the direction of induced magnetization in magnetooptical materials by changing the chiral nature of the circularly polarized input light.This magnetization field,which enables magnetization reversal rates of picosecond and even femtosecond orders of magnitude,is widely used in all-optical magnetic recording,atomic capture and confocal nuclear magnetic resonance microscopy.The researchers generated magnetization fields with higher resolution or longer focal depths or different functions by co-regulating the amplitude,phase,and polarization characteristics of the input light or by increasing the numerical aperture of the focusing lens.On the other hand,anisotropic materials have been widely used in areas such as all-optical magnetic recording in order to preserve record information for a longer and more stable period of time.However,theoretical studies on the properties of the magnetization field in anisotropic materials,the birefringence effect and the effect of the interface on the magnetization field are not yet complete.In this thesis,from the perspective of the practical application of all-optical magnetic recording,an in-depth study is carried out around the properties of tightly focused vector light-induced magnetization fields in single-axis crystals,as follows.First,the theory of vector light tight focus at high numerical apertures and the inverse Faraday effect principle are described in detail,and the distribution characteristics of several vector vortex beam-induced magnetization fields are numerically simulated and summarized.Secondly,In view of the fact that the existing research on the magnetization field is limited to isotropic media,and in combination with the practical problems of anisotropic optical properties of all-photomagnetic recording materials,theoretically the tight-focusing properties and the inverse Faraday effect in anisotropic monoaxial crystal materials have been studied in depth,and the equations for the columnsymmetric vector light-focusing focal field distribution and magnetization field distribution in anisotropic monoaxial crystals have been derived,and the differences between the magnetization field in isotropic media and the magnetization field in anisotropic monoaxial crystals have been analyzed by comparison.Finally,in order to meet the practical needs of practical engineering in the all-optical magnetic recording field of super-resolution and long focal depth,the input optical field amplitude or phase modulation is optimized,and the binary diffraction optics are optimized according to the genetic algorithm,so that the transverse resolution beyond the diffraction limit of the magnetization field and the needle-shaped magnetization field distribution are realized.Optimized phase and amplitude modulation and vortex multiplexing modulation,for applications such as multi-layer or multi-region recording of information and screening or capture of magnetic particles,the generation of spatially multiple spot and flap magnetization fields in single-axis crystals is achieved.