Hemispherical Digital Condenser Research Articles

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-varied 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 × /0.1NA objective due to the geometric constraint with the declined illumination intensities and attenuated signal-to-noise ratio (SNR). Thus the highest achievable half-pitch resolution is usually constrained between 500-1000 nm, which cannot meet the requirements of high-resolution biomedical imaging applications. Although it is possible to improve the resolution by using a high-NA objective lens, the FP approach is less appealing as the decrease of field-of-view (FOV) will far exceed the improvement of spatial resolution in this case. 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 × /0.1NA objective with the final effective imaging performance of 1.05NA at a half-pitch resolution of 244 nm with the incident wavelength of 465 nm across a wide FOV of 14.60 mm2, corresponding to a SBP of 245 megapixels. Our work provides an essential step of FP towards high-throughput imaging applications.

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.

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.

Imaging photonic crystals using Fourier plane imaging and Fourier ptychographic microscopy techniques implemented with a computer controlled hemispherical digital condenser

Fourier plane imaging (FPIM) and Fourier ptychographic (FPM) microscopy techniques were used to image photonic crystals. A computer-controlled hemispherical digital condenser provided required sample illumination with variable inclination. Notable improvement in image resolution was obtained with both methods. However, it was determined that the FPM technique cannot surpass the Rayleigh resolution limit when imaging photonic crystals.

Fourier ptychographic microscopy using an infrared-emitting hemispherical digital condenser.

Fourier ptychographic microscopy is demonstrated in the near-infrared spectral range using a computer-controlled hemispherical digital condenser comprising multiple 940 nm wavelength light emitting diodes. This technique was used to image periodic patterned samples (photonic crystals). Experimental and simulated results using a phase retrieval algorithm were found to be in excellent correspondence. We show that for samples with a single period in each direction, the resolution of the obtained high-resolution near-infrared images is limited by the Rayleigh criteria.

Super-resolution imaging of photonic crystals using the dual-space microscopy technique

We present an experimental implementation of the recently proposed dual-space microscopy (DSM), an optical microscopy technique based on simultaneous observation of an object in the position and momentum spaces, using computer-controlled hemispherical digital condensers. We demonstrate that DSM is capable of resolving structures below the Rayleigh resolution limit.

Versatile optical microscopy using a reconfigurable hemispherical digital condenser.

We present a computer-controlled hemispherical digital condenser and demonstrate that a single device can be used to implement a variety of both well established and novel optical microscopy techniques. We verified the condenser capabilities by imaging fabricated periodic patterned structures and biological samples.