High-resolution Observation With a Conventional Optical Microscope Using Ring Illumination

Standard optical microscopes are commonly used in research, education, development, and manufacturing. The spatial resolution limit of a standard optical microscope is approximately 200 nm, about half the wavelength of light. Due to this limitation, observations of higher resolution have required the use of expensive and complex optical microscopes with specialized optics. Here, we report that by using ring-shaped transmitted light in a conventional optical microscope, it is possible to directly observe samples with a high spatial resolution of less than 200 nm. By observing 100 nm-diameter polystyrene (PS) beads and a thin carbon film, we achieved a spatial resolution of approximately 160 nm with our current system. The mechanism by which ring light achieves improved spatial resolution compared to normal light is thought to be because the incident angle of the transmitted light is added to the numerical aperture of the objective lens. This system is extremely simple, requiring only a commercially available, inexpensive ring-shaped light source to be placed on an optical microscope, and does not require any special image information processing. This method facilitates high-resolution observation of materials, emulsions, and biological samples, and is expected to be applied to a variety of scientific and technological fields.