Center for Relativistic Laser Science

2017 ABC

In high-resolution microscopy, objective lenses with high numerical aperture (NA) are essential elements. Oil immersion type objectives are widely exploited to achieve extremely high NA. However, their relatively limited working distance of a few hundred microns, limits their imaging depth and makes them hard to be used for deep-tissue imaging.

As a solution for this issue, we exploit a pair of oil-immersion type microscope condensers (Nikon MBL78700) for both illumination and detection to set up a holographic phase microscope in transmission geometry. Since their working distance is an order of magnitude longer than that of objective lenses, our optical system is able to deliver images of relatively thick targets up to high NA. However, images delivered by these lenses are still distorted due to strong aberration. This is mainly caused by the condenser lenses.

We first acquire three sets of holographic phase images with 20 thousand different illumination directions. The number of required images depends on field of view and NA. Each set consists of images of illumination; the specimen; and a test target at a different image plane, respectively. From these data, input and output aberration maps are measured by maximizing intensity of synthetic aperture image. These maps are exploited to numerically correct the aberration of the optical system up to 1.2 NA. Our method allows diffraction-limited synthetic aperture imaging with microscope condensers.