Research on lateral resolution enhancement of structured illumination confocal scanning microscopy

Abstract

Confocal microscopy enables visualization of optical sections within thick transparent objects without physical sectioning and is used for three-dimensional imaging in the life sciences and semiconductor industries. However, like other optical microscopes, the confocal microscope has poor lateral resolution in comparison with non-optical imaging devices, such as SEM (Scanning Electron Microscopy) or AFM (Atomic Force Microscopy), which can resolve atomic-level features. The low lateral resolution of optical microscopy is caused by the well-known diffraction limit. In particular, focused light has a finite volume, the size of which is determined by the numerical aperture of the objective lens and the wavelength of light. Objects with features smaller than the volume of the focused light cannot be resolved. Generally, the lateral resolution of an optical microscope cannot exceed 200 nm. In spite of many advantages of confocal microscopy, such as high speed 3D imaging, non-destructive, non-contact measurement, and molecular imaging, the low lateral resolution has limited use of confocal microscope in diverse research and industry fields which need especially high lateral resolution. There have been many efforts to enhance the lateral resolution of the confocal microscope, such as 4Pi optics, pupil plane filters and STED. Although these imaging systems are quite effective, they are often complicated or have side-lobe problems that cause defects in the resulting images. Structured illumination techniques have also been used to enhance the lateral resolution of the conventional epi-fluorescence microscope. In a structured illumination microscope (SIM), an object with fine periodic features is illuminated by a sinusoidal structured illumination. The superposition of these two fine periodic patterns creates moir$\eacute$ fringes in which the fringe patterns can have much lower frequencies than shown by the individual pattern. This means that high-frequency inf...