Abstract
We demonstrate lensfree holographic microscopy on a chip to achieve ~0.6 µm spatial resolution corresponding to a numerical aperture of ~0.5 over a large field-of-view of ~24 mm2. By using partially coherent illumination from a large aperture (~50 µm), we acquire lower resolution lensfree in-line holograms of the objects with unit fringe magnification. For each lensfree hologram, the pixel size at the sensor chip limits the spatial resolution of the reconstructed image. To circumvent this limitation, we implement a sub-pixel shifting based super-resolution algorithm to effectively recover much higher resolution digital holograms of the objects, permitting sub-micron spatial resolution to be achieved across the entire sensor chip active area, which is also equivalent to the imaging field-of-view (24 mm2) due to unit magnification. We demonstrate the success of this pixel super-resolution approach by imaging patterned transparent substrates, blood smear samples, as well as Caenoharbditis Elegans.
Highlights
We demonstrate lensfree holographic microscopy on a chip to achieve ~0.6 μm spatial resolution corresponding to a numerical aperture of ~0.5 over a large field-of-view of ~24 mm2
To bypass this limitation, we implemented a sub-pixel shifting based super-resolution algorithm to effectively recover much higher resolution digital holograms of the objects, permitting sub-micron spatial resolution to be achieved across the entire sensor chip active area, corresponding to an imaging field-of-view of ~24 mm
Summary
Digital holography has been experiencing a rapid growth over the last few years, together with the availability of cheaper and better digital components as well as more robust and faster reconstruction algorithms, to provide new microscopy modalities that improve various aspects of conventional optical microscopes [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. In an effort to achieve wide-field on-chip microscopy, our group has recently demonstrated the use of unit fringe magnification (F~1) in lensfree in-line digital holography to claim an FOV of ~24 mm with a spatial resolution of < 2 μm and an NA of ~0.1-0.2 [15,16] This recent work used a spatially incoherent light source that is filtered by an unusually large aperture (~50-100μm diameter); and unlike most other lensless in-line holography approaches, the sample plane was placed much closer to the detector chip rather than the aperture plane, i.e., z1>>z2. Together with a large FOV, these unique features bring simplification to the set-up since a large aperture (~50μm) is much easier to couple light to and align [15,16]
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