Subwavelength resolution Fourier ptychography with hemispherical digital condensers

Fourier ptychography (FP) is a promising computational imaging technique that overcomes the physical space-bandwidth product (SBP) limit of a conventional microscope by applying angular diversity illuminations.However, to date, the effective imaging numerical aperture (NA) achievable with a commercial LED board is still limited to the range of 0.3-0.7 with a 4×/0.1NAobjective due to the constraint of planar geometry with weak illumination brightness and attenuated signal-to-noise ratio (SNR).Thus the highest achievable half-pitch resolution is usually constrained between 500-1000 nm, which cannot fulfill some needs of high-resolution biomedical imaging applications.Although it is possible to improve the resolution by using a higher magnification objective with larger NA instead of enlarging the illumination NA, the SBP is suppressed to some extent, making the FP technique less appealing, since the reduction of field-of-view (FOV) is much larger than the improvement of resolution in this FP platform.Herein, in this paper, we initially present a subwavelength resolution Fourier ptychography (SRFP) platform with a hemispherical digital condenser to provide high-angle programmable plane-wave illuminations of 0.95NA, attaining a 4×/0.1NAobjective with the final effective imaging performance of 1.05NA at a half-pitch resolution of 244 nm with a wavelength of 465 nm across a wide FOV of 14.60 mm 2 , corresponding to an SBP of 245 megapixels.Our work provides an essential step of FP towards high-NA imaging applications without scarfing the FOV, making it more practical and appealing.