Scanning diffracted-light microscopy.

Scanning the direction of the light that is diffracted by a sample permits the achievement of image diversity, which is necessary for implementing the Fourier ptychographic microscopy technique (FPM) using only perpendicular illumination. We also demonstrated that the same method allows for implementation of the illumination-direction-multiplexing FPM technique when the sample is illuminated using a ring-shaped condenser.

Subwavelength resolution scanning diffracted-light microscopy using plasmonic ultra-thin condensers.

We used a rotating slit placed at the back focal plane of the microscope's objective lens to scan the light diffracted by a plasmonic crystal, which had a period smaller than the resolution limit of the optical microscope. A set of images were collected at different orientations of the slit. A high-resolution image of the plasmonic crystal was obtained by processing the experimental images using a numerical Fourier ptychographic algorithm. Supporting simulations of the experiments are also presented.

Imaging photonic crystals using hemispherical digital condensers and phase-recovery techniques.

We describe experiments where Fourier ptychographic microscopy (FPM) and dual-space microscopy (DSM) are implemented for imaging photonic crystals using a hemispherical digital condenser (HDC). Phase-recovery imaging simulations show that both techniques should be able to image photonic crystals with a period below the Rayleigh resolution limit. However, after processing the experimental images using both phase-recovery algorithms, we found that DSM can, but FPM cannot, image periodic structures with a period below the diffraction limit. We studied the origin of this apparent contradiction between simulations and experiments, and we concluded that the occurrence of unwanted reflections in the HDC is the source of the apparent failure of FPM. We thereafter solved the problem of reflections by using a single-directional illumination source and showed that FPM can image photonic crystals with a period below the Rayleigh resolution limit.

Scanning diffracted-light photography using white-light and thermal radiation sources.

A 4-f imaging arrangement of lenses with a camera and a rotating slit placed at the Fourier plane of the system was used to obtain the optical disturbance produced by a macroscopic sample. The sample was illuminated by collimated beams from white-light and thermal radiation sources. The agreement between simulated and experimental results, obtained by processing the captured images using a Fourier ptychographic algorithm, demonstrates that scanning with the slit the direction of the light diffracted by the sample permits achieving the image diversity necessary for successful implementation of the scanning diffracted-light imaging technique.

Illumination-direction multiplexing Fourier ptychographic microscopy using hemispherical digital condensers.

Simulations were conducted to explore a broader collection of possible illumination patterns realizable using a white-light-emitting hemispherical digital condenser. Several simple, but practical, illumination patterns were selected and used in experiments where a sample was illuminated simultaneously from different directions. The illumination-direction multiplexing (IDM) Fourier ptychographic microscopy (FPM) method was successfully used for imaging and phase recovery. This study suggests that IDM-FPM can be used for imaging photonic crystals with subwavelength periods using traditional microscope condensers with variable numerical aperture.