Super-resolution Microscopic Imaging Via Polarization Modulation

Because of non-destructive and high resolution,Optical microscopy has played a more and more important role in biomedical research.However,due to the barricade by the optical diffraction limits,the common optical microscopy imaging has achieved lateral resolution of 200-300 nm and a vertical resolution of 500-600 nm,which is far from satisfying the biomedical exploration of life activities,especially in the molecular scale.super-resolution imaging technology is able to beyond the diffraction limit and has become a research hotspot.In particular,the development of fluorescence technology has opened a new door for optical super-resolution microscopic imaging technology.Such as the superresolution microscopic imaging technology of STED,PLAM,etc.has been developed based on fluorescence intensity modulation,the resolution of optical microscopy is increased to several tens of nanometers.Polarization,as a fundamental property of fluorescence,provides another dimension of high contrast in microscopic imaging techniques besides intensity contrast.Mainly based on the fact that the absorption probability depends on orientation difference between the absorbing dipole and exciting electric field and the polarization of emission field,this technique is applied to obtain the direction information of the fluorescent molecules and then is successfully used to detect the direction and structure information of the biomolecule.In this thesis,based on the sensitivity of the fluorescence absorption efficiency to the polarization direction of the excitation light,we explored the super-resolution microscopy imaging via polarization modulation.In the study,Firstly,we use incident light with different polarization directions to excite the sample,and obtain the polarization-modulated fluorescence images sequence.Then the Fourier transform is carried out along the polarization direction to discriminate fluorescent molecules.The results show that the polarization modulation is contribute to molecules discrimination.Further we performed super-resolution reconstruction on the acquired polarization modulated images sequence by the polarization-modulated conjugate gradient method(P-CG).The reconstructed images demonstrate that the fluorescence polarization modulation can increase the image sparsity,and its resolution depends on the fluorescent molecule orientation difference,~50nm resolution can be achieved with orientation difference greater than70° in Wide field microscopy and orientation difference greater than30° in confocal microscopy.Finally,based on the coherent superposition of linear and radial polarized light,we realized the arbitrary control for three-dimensional polarization direction in the focusing light field of an objective.By performing the polarization modulation outside the sample plane,we realized the super-resolution imaging for molecules with orientation difference outside the sample plane.