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We present deep-ultraviolet Fourier ptychography (DUV-FP) for high-resolution chemical imaging of biological specimens in their native state without exogenous stains. This approach uses a customized 265-nm DUV LED array for angle-varied illumination, leveraging the unique DUV absorption properties of biomolecules at this wavelength region. We implemented a robust feature-domain optimization framework to overcome common challenges in Fourier ptychographic reconstruction, including vignetting, pupil aberrations, stray light problems, intensity variations, and other systematic errors. By using a 0.12 numerical aperture low-resolution objective lens, our DUV-FP prototype can resolve the 345-nm linewidth on a resolution target, demonstrating at least a four-fold resolution gain compared to the captured raw images. Testing on various biospecimens demonstrates that DUV-FP significantly enhances absorption-based chemical contrast and reveals detailed structural and molecular information. To further address the limitations of conventional FP in quantitative phase imaging, we developed a spatially coded DUV-FP system. This platform enables true quantitative phase imaging of biospecimens with DUV light, overcoming the non-uniform phase response inherent in traditional microscopy techniques. The demonstrated advancements in high-resolution, label-free chemical imaging may accelerate developments in digital pathology, potentially enabling rapid, on-site analysis of biopsy samples in clinical settings.
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Spatially‐Coded Fourier Ptychography: Flexible and Detachable Coded Thin Films for Quantitative Phase Imaging with Uniform Phase Transfer Characteristics
Abstract Fourier ptychography (FP) is an enabling imaging technique that produces high‐resolution complex‐valued images with extended field coverages. However, when FP images a phase object with any specific spatial frequency, the captured images contain only constant values, rendering the recovery of the corresponding linear phase ramp impossible. This challenge is not unique to FP but also affects other common microscopy techniques — a rather counterintuitive outcome given their widespread use in phase imaging. The underlying issue originates from the non‐uniform phase transfer characteristic inherent in microscope systems, which impedes the conversion of object wavefields into discernible intensity variations. To address this challenge, spatially‐coded Fourier ptychography (scFP) is presented for true quantitative phase imaging. In scFP, a flexible and detachable coded thin film is attached atop the image sensor in a regular FP setup. The spatial modulation of this thin film ensures a uniform phase response across the entire synthetic bandwidth. It improves reconstruction quality, corrects refractive index underestimation issues prevalent in conventional FP, and adds a new dimension of measurement diversity in spatial domain. The development of scFP is expected to catalyze new research directions and applications for phase imaging, emphasizing the need for true quantitative accuracy with uniform frequency response.
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- Award ID(s):
- 2012140
- PAR ID:
- 10522347
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 12
- Issue:
- 15
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract High-resolution transmission electron microscopy (HRTEM) is an important method for imaging beam sensitive materials often under cryo conditions. Electron ptychography in the scanning transmission electron microscope (STEM) has been shown to reconstruct low-noise phase data at a reduced fluence for such materials. This raises the question of whether ptychography or HRTEM provides a more fluence-efficient imaging technique. Even though the transfer function is a common metric for evaluating the performance of an imaging method, it only describes the signal transfer with respect to spatial frequency, irrespective of the noise transfer. It can also not be well defined for methods, such as ptychography, that use an algorithm to form the final image. Here we apply the concept of detective quantum efficiency (DQE) to electron microscopy as a fluence independent and sample independent measure of technique performance. We find that, for a weak-phase object, ptychography can never reach the efficiency of a perfect Zernike phase imaging microscope but that ptychography is more robust to partial coherence.more » « less
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ABSTRACT Linear phase‐contrast scanning transmission electron microscopy (STEM) techniques compatible with high‐throughput 4D‐STEM acquisition are widely used to enhance phase contrast in weakly scattering and beam‐sensitive materials. In these modalities, contrast transfer is often suppressed at low spatial frequencies, resulting in a characteristic contrast gap that limits contrast. Approaches that retain low‐frequency phase contrast exist but typically require substantially increased experimental complexity, restricting routine use. Dark‐field STEM imaging captures this missing low‐frequency information through electrons scattered outside the bright‐field disk, but discards a large fraction of the scattered signal and is therefore dose‐inefficient. Fused Full‐field STEM (FF‐STEM) is introduced as a 4D‐STEM imaging modality that overcomes these limitations by combining ptychographic phase reconstruction with tilt‐corrected dark‐field imaging within a single acquisition. Bright‐field data are used to estimate probe aberrations and reconstruct a high‐resolution phase image, while dark‐field data provide complementary low‐frequency contrast. The two channels are fused in Fourier space using Wiener‐band weighting based on the spectral signal‐to‐noise ratio, yielding transfer‐gap‐free images with high contrast. FF‐STEM preserves the upsampling and depth‐sectioning capabilities of ptychography, adds robust low‐frequency contrast characteristic of dark‐field imaging, and enables dose‐efficient, near–real‐time reconstruction.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/adom.202303028
