Investigation On The Regulation Of Optical Needles And Light-induced Magnetization Fields

In the past two decades,with the optical applications in various fields,research on the regulation of optical needles and light-induced magnetization fields has aroused widespread concern.Optical needles and light-induced magnetization fields are not only applied in classic applications such as optical storage,high-resolution imaging,material processing,all-optical recording,and ferromagnetic semiconductor device development,but also in the field of quantum entanglements and quantum communications.The key and basic research of optical needles and light-induced magnetization fields is how to achieve super-resolution lateral dimensions and adjustable longitudinal depth.Therefore,optimizing the design of the focusing system and exploring the tight focus characteristics of the cylindrical vector beam have the same important practical significance.In this thesis,based on the vector diffraction theory and the inverse Faraday effect?IFE?,we study the regulation of the optical needles and the light-induced magnetization fields under different focusing mirror systems by the modulation of the wavefront of the cylindrical vector beam by special phase diffractive elements.Several achievements and contributions are summarized:Starting from the binary phase diffractive optical element?DOE?with multi-belts,the focusing system is divided into four parts:polarization modulation,amplitude modulation,phase modulation and focusing objective.The influence of each part on the focusing system is elaborated.A parabolic mirror is selected as the focusing objective,and a novel DOE with three-belts is designed to modulate the radially polarized Bessel Gaussian?BG?beams.The focusing system can be used to achieve a super-resolution longitudinally polarized optical needle.Based on the eigenvalues such as the lateral dimension,the longitudinal depth of focus and the longitudinal field power ratio of the longitudinally polarized optical needle,Theoretically explaining why the three-belts is the minimum number of DOE that modulating the radially polarized BG beams.Further,the focusing system is described as a whole function from the mathematical point of view,and some properties of the system function are preliminarily analyzed.It is difficult for multi-belts DOE modulation to compromise the lateral size and longitudinal depth of focus of the optical needle.Based on the parabolic mirror,a focusing system using the ring-shaped amplitude filter and the spiral phase plate to co-modulate azimuthally polarized Gaussian beams is proposed.The pure transversely polarized optical needle with super-resolution and ultra-long focus depth can be realized,and theoretical simulation results are given.Innovative analytical mathematical methods for analyzing electromagnetic fields in the focal region and the expression of the approximate relationship between the depth of focus and the annular incident angle??is established.The influence of different??values on the depth of focus is analyzed.The strict proof of the controllability of the depth of focus is given.Based on the inverse Faraday effect of uniform magneto-optical film,a method to realize pure longitudinal polarized magnetization needle with super-resolution and ultra-long focus depth is proposed,and the theoretical simulation results are given.The influence of different??values on the transverse dimension and longitudinal depth of pure longitudinal polarized magnetization needle is analyzed.The controllability of the magnetization needle is discussed.More importantly,the magnetization needle and the optical needle have the same longitudinal depth,though their distribution is different.The magnetization needle exhibits less oscillatory behavior with side lobes in the transverse direction.Re-examining the focusing system functions described in the previous chapters,it is found that in the same numerical aperture,the lateral dimension and longitudinal depths of the optical needle and the magnetization needle are not changed by the selection of the focusing objective.In other words,the size characteristic values of the optical needle and the magnetization needle are independent of the apodization function of the focusing objective.Based on the focusing theory of elliptical mirror,the focusing system to generate optical needle and magnetization needle with tunable longitudinal depth by focusing a narrow annulus of azimuthally polarized beams using optmagnetic materials and an elliptical mirror is proposed.In addition,compared with parabolic mirror based system,the elliptical mirror based focusing technique is potentially promising in aberration control of incident beam when the aperture of mirror is enlarged to adapt a large stage or specimen container at a small beam shading ratio and the two aberration free focal points inside of elliptical mirror might be helpful to construct a fast point scanning microscopy by using well developed scanning techniques at F₁.The application prospect of elliptical mirror based focusing technique has been greatly expanded.The unique specialties such optical needle and magnetization needle possess implies that this method could be adopted in a wide range of practical domain,such as optical manipulation,photolithography,controlling light–mater interaction in magnetic materials as well as for developing novel optomagnetic devices,especially two-photon polymerization technology to realize resolution beyond the diffraction limit and ultrahigh density all-optical magnetic recording...