Investigation Of Photonic Jet Generated By Dielectric Particle Illuminated By A Shaped Beam

The optical microscope can observe undamaged living samples in the natural growing environment.However,the resolution limit of conventional optical microscopy is not better than 200 nm in the visible light wavelength range(400-750nm),which is limited by the Abbe diffraction limit.With the development of biological research from the whole species level to the molecular level,how to improve the spatial resolution of optical microscopes has become a key issue to be solved urgently,which is of great significance to the development of life science and other fields.Breaking the diffraction limit has become an important opportunity and challenge faced by researchers at home and abroad,it is one of the most important frontier basic studies in current research.In recent years,great development of microscopic imaging technology has been achieved based on scanning fluorescent tags,artificial material preparation of super lens,surface plasmon amplification of evanescent wave and micro-nano ball super diffraction imaging technology due to the reveal of new mechanism of interaction between the light and matter(fluorescent molecules,metal film layer materials,etc.)and the development of high sensitivity of the detector.Among them,the super-resolution microscopy technology assisted by microparticles can effectively break through the diffraction limit and achieve super-resolution of more than one tenth of the wavelength,which has attracted attentions from lots of researchers.Although the imaging mechanism based on microparticle assisted super-resolution microscopy is not completely clear,it has become a consensus that photonic jets formed by microsphere lens with high intensity,small transverse width and long propagation distance play an important role on the imaging procedure.By changing the size,refractive index,shape and structure of the microsphere,as well as the wavelength,intensity distribution and polarization of the incident beam,the characteristics of the photonic jet can be mannipulated in a large extent.How to optimize the characteristics of the photonic jet has become a research hotspot and a key issue in super-resolution imaging.In this paper,based on the Generalized Lorenz-Mie Theory(GLMT)and the Finite-Difference Time-Domain Method(FDTD),the photonic jet properties of spherical particles(uniform spheres,double spheres,eccentric spheres)and ellipsoid particles under the incident of typical shaped beams(Gaussian beam,Bessel beam,Laguerre-Gaussian beam)are investigated.The effects of various beam parameters and particle parameters on the characteristics of photonic jet are analyzed in detail,which provides a theoretical basis for optimizing the characteristics of photonic jet and provides a support for revealing the imaging mechanism of microsphere assisted super-resolution microscopy.The main research work of this paper includes:1.The Generalized Lorenz-Mie Theory for the interaction between spherical particles and shaped beams is analyzed.Based on the FORTRAN 90,the numerical programming of the interaction analysis between spherical particles and typical shaped beams(Gaussian beam,Bessel beam)is realized.Then,(a)the photonic jet characteristics of eccentric spherical particles under plane wave incidence are analyzed in detail,and the influence of the degree of eccentricity of the particle on the main parameters of photonic jet characteristics(peak intensity,working distance,position,FWHM,etc.)is studied.(b)The photonic jet characteristics of the microsphere lens under the incidence of Gaussian beam and Bessel beam are analyzed in detail.The effects of beam parameters such as the beam waist radius and center position of Gaussian beam,the half-cone angle and polarization of Bessel beam on the photonic jet characteristics are studied in detail.The simulation results show that the characteristics of the photonic jet can be greatly controlled by changing the particle structure,optical refractive index or parameters of the incident beam.2.The Finite-Difference Time-Domain(FDTD)method for the interaction between non-spherical particles and shaped beams is analyzed,and the numerical algorithm for the interaction between non-spherical particles and shaped beams is realized by reconstructing the typical shaped beams in the FDTD algorithm.By comparing the results of the proposed algorithm with the GLMT,the correctness of the algorithm and program is verified.Then,a detailed analysis of photonic jet characteristics of micro ellipsoid lens excited by the Gaussian beam,the Bessel beam and Laguerre-Gaussian beam are performed:(a)As the long axis and short axis changes,the effect of ellipsoid shape on the photonic jet characteristics are analyzed in detail.(b)Through the numerical simulation of photonic jets of ellipsoid particles generated by the Gaussian beam,Bessel beam and Laguerre-Gaussian beam incidence,the effects of beam parameters such as beam waist radius of Gaussian beam,half-cone angle and polarization characteristics of Bessel beam,angular index and radial index of Laguerre-Gaussian beam on photonic jet characteristics are studied.The results show that the shape of the particles and the parameters of the incident beam have important effects on the characteristics of the photon jet.