| In recent years,with the further development of life science research,higher and higher requirements have been put forward for the imaging resolution of optical microscopes.The proposal of a series of super-resolution imaging technologies breaks through the diffraction limit,and pushes the resolution of optical microscopes to a smaller scale.Among them,the dielectric microsphere super resolution technology has received extensive attention due to its high-intensity subwavelength focusing(Hot Spot and Photonic Nanojet).However,it also has defects.First of all,the focusing ability of traditional microspheres with single refractive index is limited,most of which are above100 nanometers.And improvement in the resolution of super-resolution imaging of microspheres is limited and its mechanism is not clear yet;second,the focal length of the microsphere is about a few wavelengths,which makes the microsphere very close to the sample,unable to image in the far field,and the field of view is small;last,in the actual use of microspheres,there are problems such as difficult processing,inaccurate positioning,and difficult operation.In this context,this paper focuses on the problems existing in the above microsphere super-resolution technique.Firstly,a high refractive index cladding and symmetric embedded structures are used to compress the focused beam of the microcylinder to below 100 nm.Then,based on the cubic microcylinder configuration,a micro/nano array structure that is easy to process and use is proposed.Finally,a curved truncated microcylinder structure is proposed to increase the effective length of photon nanojet The detailed research contents are as follows:1.Ultra narrow focusing characteristics of the focused beams of microcylinder is investigated.A microcylinder structure design method that can realize ultra narrow localized beam is proposed,and an ultra narrow localized beam with a full width at half maximum of the microcylinder focusing spot of 66.70nm(λ/8.47)is obtained.The interference superposition caused by local modes modulation explains how to further compress the beam width of the localized beam and guide beam emission.Numerical analysis shows: when the volume and shell radius of the microcylinder are fixed,the overall highest resonant mode of the microcylinder depends on the refractive index of the inner core and the shell,the local modes of embedded parts and the main mode of the microcylinder together form the minimum width of localized beam.Changing the embedded height h regulates destructive interference to shrink waist.It is found that FWHM is positively correlated with the local structural parameters within the change range of h of 20 nm.Reducing the refractive index of local structures can increase the effective length to make localized beam gradually extend outwards.Further compressing the width of the focused beam can improve the accuracy of laser processing based on microcylinders and the resolution of scanning microsphere superresolution imaging systems.2.Two kinds of localized beams: hot spot and photonic nanojet,which exist in the microcylinder are studied.It is found that two kind of beams can be transformed to each other under the modulation of refractive index and local parameter.The design method of shortening beam width is verified based on the gradient index microcylinder.At the same time,several physical phenomena,such as WGM effect,local standing wave interference,multi-beam emission,optical hook and directional emission are studied in simulation.The variation law and formation mechanism of each physical phenomenon with the microcylinder structure parameters are explored,and the reasonable physical explanations are given.3.Aiming at the problems existing in its practical use,a micro cubic array with single refractive index which is easy to process and use is proposed.The array structure is successfully processed by two-photon 3D printing technology.After experimental testing,the characteristics of the waist of the focused beam of experimental results and simulation results are basically same.Based on the beam width shortening strategy,the double layer cubic microcylinder array structures with high refractive index and low refractive index are designed,respectively.And the influence of core parameters on the characteristics of the focused beam are explored.The method of cubic and its array can effectively solve the problem of difficult fixation and precise manipulation of single microsphere.The method of cubic microcylinder and their arrays can effectively solve the problems of single microspheres being difficult to fix and operate,promoting the practicality of microcylinder super-resolution technology.4.The ultralong effective length characteristics of the photonic nanojet are studied.Aiming at the defect of short effective length and working distance of photonic nanojet,a structural design method with an ultralong effective length of the dynamically tunable photonic nanojet is proposed.By changing the configuration of the second interface and the distance between the two interfaces,the energy flow at the focal point tends to be parallel.The effective length of the nanojet can reach 209.49λ.Effectively solving the problem of short effective length and working distance of photon nanojet,expanding the application range of microspheres.Similar results can be obtained by substituting discretized microcylinder,and two easy-to-use structural design is proposed.A set of microsphere super-resolution detection optical system is built,using barium titanate microspheres to carry out super-resolution imaging and detection experiments on fluorescent nanospheres of about 100 nm,the detection of fluorescent nanospheres is realized through the built rear-end microscopic imaging optical path.Carry out research on the characteristics of microcylinder coupling evanescent wave as propagating wave.Under the two conditions of evanescent wave generation,the transformation ability of microcylinder and cubic microcylinder are explored,respectively.The factors of the refractive index of microcylinder,incident light phase,scattering of Au nanoparticles on the transformation ability is studied. |
