Research On Imaging Characteristics Based On High Refractive Index Microspheres

The resolution of optical microscope can only reach about half of the wavelength due to Abbe diffraction limit.Super-resolution imaging can be achieved by microsphere assisted optical microscope.Microsphere-assisted microscopy imaging techniques have attracted much attention because they do not require fluorescent labeling of samples and have no phototoxicity.In order to reveal the mechanism of super-resolution imaging of microspheres,this paper focuses on the imaging of high refractive index barium titanate（Ba Ti O₃ Glass,BTG）microspheres,as follows:1.Based on Snell’s law and boundary conditions,this paper theoretically analyzes the process by which microspheres convert evanescent waves into propagation waves,and studies the influence of the refractive index of microspheres and immersion medium on imaging characteristics of microspheres.The research shows that high refractive index BTG microspheres have higher lateral magnification than low refractive index silica（Si O₂）microspheres and polystyrene（PS）microspheres.In addition,the imaging characteristics of BTG microspheres on sub-wavelength objects under different immersion environments（water,SU8-2002,alcohol,Polydimethylsiloxane and pine oil）are also experimentally studied.At the same time,the Finite Difference Time Domain simulation software is used to study the imaging mechanism of BTG microspheres,and it finds that the immersion medium with a higher refractive index will reduce the imaging magnification of the microspheres due to the increase of the object focal length of the microspheres.2.The imaging characteristics of cascaded microsphere lenses are studied.The primary imaging system is Si O₂ or PS microsphere array,and the secondary imaging system is high refractive index BTG microsphere.The imaging characteristics of Si O₂/BTG and PS/BTG cascaded microspheres when the size of Si O₂ or PS microspheres in the primary imaging system are changed are studied.The study find that the magnification of PS/BTG cascaded microsphere structure is better than that of Si O₂/BTG cascaded microsphere structure at the same size.As the size of the microspheres in the primary imaging system changed from 400nm to 900 nm,the imaging magnification of cascaded microsphere structures increases,and the imaging magnification of the two cascaded microsphere structures are greater than that of the BTG microspheres when imaged alone,and the imaging magnification can be increased up to 1.46 times.3.Metal nano-dots with subwavelength structures are prepared by using microsphere arrays,and the optical characteristics of the metal nanoparticles in the metal nano-dots are simulated.Finally,the BTG microsphere-assisted microscopy technology is used to image metal nano-dots with subwavelength structures.In the wavelength from 400 nm to 900 nm,it finds that the optical properties of Au,Ag,and Al metal nanoparticles of the same geometric size are different.When the size of the metal nanoparticles increases,the peak position is red-shifted and the intensity of the scattering spectrum becomes larger.The intensity of the scattering spectrum becomes larger.Among them,the scattering intensity of the Ag and Al metal nanoparticles is higher than that of the Au metal nanoparticles,and different scattering characteristics result in different imaging resolutions.Therefore,in the experiment,the Ag and Al metal nanoparticles with a distance of 150 nm between two adjacent metal nanoparticles can be successfully resolved,while the Au metal nanoparticles cannot be resolved.