Research On The Characteristics Of Super-resolution Imaging With Cascade Microsphere Lens

Microscopy is widely used in scientific research of many disciplines,since the microscopic objects can be observed by a conventional optical microscopy.The resolution of a optical microscopy is about ?/2 due to Abbe's diffraction limit.In order to visualize features smaller than ?/2,many super-resolution imaging approaches have been proposed.Among these techniques,microspheres have provided us with an effective and simple method to obtain super-resolution imaging under white light illuminated optical microscopy and have attracted the research interests of many groups.In microsphere studies,only one microsphere is used,and the improvement in the magnification of a microsphere is due to the increased refractive index of the microsphere.With a constant relative refractive index,a cascaded microsphere lens is designed for improving the super-resolution capability of a microsphere,and the imaging properties of are studied in this paper.The main research of the thesis is as follows:First,a microsphere-surrounded type cascaded microsphere lens is proposed,and the imaging properties of the cascaded microsphere lens and a single silica microsphere are studied.Here,the immersion medium is ethanol.The experimental results show that the magnification of the cascaded microsphere lens is about 1.44 times greater than that of the single silica microsphere,while the field of view of the cascaded microsphere lens is decreased.Studies reveal that the two microsphere layers of the cascaded microsphere lens contribute to the final amplification;the focal position of the cascaded lens microsphere must be close to the sample in order to observe it;the center of the two microspheres is in a line to get a bright and clear image in the middle;the size of the first lens limits the field of view of the cascaded microsphere lenses.Then,a spin coating type cascaded microsphere lens is designed,and the imaging properties of the cascaded microsphere lens and a single silica microsphere are studied.Here,the immersion medium is SU8-2002.The experimental results show that the magnification of the cascaded microsphere lens is about 1.38 times greater than that of the single silica microsphere,while the field of view of the cascaded microsphere lens is decreased.In addition,an special phenomenon in imaging of the cascaded microsphere lens is observed:one is that only the middle region has an image and the magnification increases,the other is that only the peripheral area has an image and the magnification is consant.Studies reveal that this cascaded microsphere lens is more easily prepared and utilized;the center of the two microspheres is in a line to improve the magnification;the smaller the full width at half maximum(FWHM),the better the super-resolution of microspheres.Finally,the structure of the spin coating type cascade microsphere lens is applied to high refractive index BaTiO3(BTG)microspheres,the imaging properties of the cascaded microsphere lens and a single BTG microsphere are studied.The single BTG microsphere is fully immersed in SU8-2002,microscale immersion oil,polydimethylsiloxane(PDMS),ethanol,and water to observed objects,respectively.Numerical simulations show that the relative refractive index is between 1.2-1.45,with the increasing of the relative refractive index,the magnification of microsphere is improved,the distance of focus and sample surface is reduced,and the FWHM is diminished.Taking into account the properties of the five types of immersion media,PDMS is regarded as the best immersion medium for cascaded high refractive index microspheres.The experimental results show that the magnification of the cascaded microsphere lens is about 1.35 times greater than that of the single silica microsphere.The narrower beam waist of the photonic nanojet can promote super-resolution ability of the microsphere.