Computational Oblique Illumination Microscopy With Isotropic High Resolution

Abstract

Although various advanced super-resolution microscopies have been developed, conventional microscopes are still the most widely used. Therefore, it is still one of the goals of light microscopists to improve the imaging performance of conventional microscopes. Ernst Abbe had proven the resolution of a bright-field microscope can be improved by oblique illumination in 1873, but the approach has not been widely applied in practice due to the intrinsic drawback that the lateral resolution of the image is anisotropic. In this article, computational oblique illumination microscopy (COIM) is proposed to isotropically improve lateral resolution. Benefiting from outstanding performance of light emitting diodes (LEDs), the programmable symmetrical oblique illumination by LEDs can easily be implemented. COIM uses symmetrical oblique illuminations to enhance the absorption contrast and weaken the phase contrast in images; then an iterative algorithm is used to fuse an image with the isotropic high lateral resolution. Unlike synthetic aperture imaging, COIM does not require phase involvement, so there are no troublesome phase detection schemes. The experimental results indicate that COIM can resolve Element 6 in Group 11 (bar or space width 137 nm) of a USAF test target using a high numerical aperture (NA) objective lens (NA = 1.25) and oblique-illumination sources (center wavelength 520 nm). The proposed technique provides a new way to improve the resolution of bright-field microscope.