Research On Influencing Factors Of Microlens Super-resolution Imaging

The resolution of a traditional optical microscope can only reach about ?/2,and super-resolution imaging by microsphere-assisted optical microscopy is a very simple method for visualizing nanoscale structures.In this thesis,the influence of the shape of the microspheres,the degree of immersion of the microspheres,and the surface properties of the samples are studied,and we attempt to find ways to improve their imaging properties.The main contents of the thesis are described as follows:1.First,we report the effects of silver films with different surface roughnesses coated on the surface of the samples on the imaging properties of BaTiO3(BTG)microspheres.Using a 15-?m-diameter BTG microsphere to observed both the 250-nm-diameter and 580-nm-diameter microsphere arrays,when the surface roughness of the silver film is increased from 3.23 to 6.80 nm,the imaging range of the BTG microsphere is expanded.Moreover,the 200-nm-diameter microsphere array can also be clearly distinguished.We propose that the scattering and the local field enhancement effect of surface plasmon polaritons caused by the rough silver layer allow more high-frequency information of the object to be coupled into the microsphere,which improves the resolution and imaging range of the microsphere.2.Second,we use SU-8 resist(n=1.60)as the immersion medium,and spin coat the surface of polystyrene(PS,n=1.60)microspheres with SU-8 resist at different speeds.As the spin speed changes,we can change both the shape of the microsphere and the immersion level of the microsphere simultaneously,obtain microlenses A,B,and C.It is found that microlenses A,B,and C can clearly distinguish stripe arrays with a period of 300 nm and a gap of 100 nm,but the imaging magnification is different.The imaging magnification of the microlens B(h/d=0.5)is the largest,which is 3.3 ×?5.2 ×.Moreover,microlens B can distinguish the arrays of Ag dots with a separation of 150 nm while the other two microlenses cannot.The simulated results by COMSOL indicate that microlens B has the minimum full width at half-maximum(FWHM)of the photonic nanojet(PNJ).The results simulated by ZEMAX show that the spherical aberration of microlens B is significantly lower than that of a microsphere microlens D.3.Third,we use the hydrofluoric acid to etch the fiber to prepare cylindrical microlenses of different sizes.Then the microlens is used to observe the stripes of a Blu-ray disc and a DVD disc.It is found that the stripes of the DVD disc can be clearly distinguished,but that of Blu-ray disc cannot be distinguished.By analyzing the results of COMSOL software simulation,we propose that the cylindrical microlens fails to realize super-resolution imaging because the fiber is not uniformly corroded by hydrofluoric acid etching,which makes the surface uneven.