25,903 research outputs found
High-throughput intensity diffraction tomography with a computational microscope
We demonstrate a motion-free intensity diffraction tomography technique that enables direct inversion of 3D phase and absorption from intensity-only measurements for weakly scattering samples. We derive a novel linear forward model, featuring slice-wise phase and absorption transfer functions using angled illumination. This new framework facilitates flexible and efficient data acquisition, enabling arbitrary sampling of the illumination angles. The reconstruction algorithm performs 3D synthetic aperture using a robust, computation and memory efficient slice-wise deconvolution to achieve resolution up to the incoherent limit. We demonstrate our technique with thick biological samples having both sparse 3D structures and dense cell clusters. We further investigate the limitation of our technique when imaging strongly scattering samples. Imaging performance and the influence of multiple scattering is evaluated using a 3D sample consisting of stacked phase and absorption resolution targets. This computational microscopy system is directly built on a standard commercial microscope with a simple LED array source add-on, and promises broad applications by leveraging the ubiquitous microscopy platforms with minimal hardware modifications
Learning Wavefront Coding for Extended Depth of Field Imaging
Depth of field is an important factor of imaging systems that highly affects
the quality of the acquired spatial information. Extended depth of field (EDoF)
imaging is a challenging ill-posed problem and has been extensively addressed
in the literature. We propose a computational imaging approach for EDoF, where
we employ wavefront coding via a diffractive optical element (DOE) and we
achieve deblurring through a convolutional neural network. Thanks to the
end-to-end differentiable modeling of optical image formation and computational
post-processing, we jointly optimize the optical design, i.e., DOE, and the
deblurring through standard gradient descent methods. Based on the properties
of the underlying refractive lens and the desired EDoF range, we provide an
analytical expression for the search space of the DOE, which is instrumental in
the convergence of the end-to-end network. We achieve superior EDoF imaging
performance compared to the state of the art, where we demonstrate results with
minimal artifacts in various scenarios, including deep 3D scenes and broadband
imaging
Standing-wave-excited multiplanar fluorescence in a laser scanning microscope reveals 3D information on red blood cells
Standing-wave excitation of fluorescence is highly desirable in optical
microscopy because it improves the axial resolution. We demonstrate here that
multiplanar excitation of fluorescence by a standing wave can be produced in a
single-spot laser scanning microscope by placing a plane reflector close to the
specimen. We report that the relative intensities in each plane of excitation
depend on the Stokes shift of the fluorochrome. We show by the use of dyes
specific for the cell membrane how standing-wave excitation can be exploited to
generate precise contour maps of the surface membrane of red blood cells, with
an axial resolution of ~90 nm. The method, which requires only the addition of
a plane mirror to an existing confocal laser scanning microscope, may well
prove useful in studying diseases which involve the red cell membrane, such as
malaria.Comment: 15 pages, 4 figures; changed the discussion of narrow-band detected
fringes (Fig. 3) to describe the phenomenon as a moire pattern between the
excitation and emission standing-wave fields, rather than a beats pattern;
added DiI(5)-labelled red blood cell in Fig. 4 to show that standing-wave
fringes are present even when the dye excitation wavelength is outside the
haemoglobin absorption ban
Multiwavelength polarization insensitive lenses based on dielectric metasurfaces with meta-molecules
Metasurfaces are nano-structured devices composed of arrays of subwavelength
scatterers (or meta-atoms) that manipulate the wavefront, polarization, or
intensity of light. Like other diffractive optical devices, metasurfaces suffer
from significant chromatic aberrations that limit their bandwidth. Here, we
present a method for designing multiwavelength metasurfaces using unit cells
with multiple meta-atoms, or meta-molecules. Transmissive lenses with
efficiencies as high as 72% and numerical apertures as high as 0.46
simultaneously operating at 915 nm and 1550 nm are demonstrated. With proper
scaling, these devices can be used in applications where operation at distinct
known wavelengths is required, like various fluorescence microscopy techniques
Near-Limb Zeeman and Hanle Diagnostics
"Weak" magnetic-field diagnostics in faint objects near the bright solar disk
are discussed in terms of the level of non-object signatures, in particular, of
the stray light in telescopes. Calculated dependencies of the stray light
caused by diffraction at the 0.5-, 1.6-, and 4-meter entrance aperture are
presented. The requirements for micro-roughness of refractive and reflective
primary optics are compared. Several methods for reducing the stray light (the
Lyot coronagraphic technique, multiple stages of apodizing in the focal and
exit pupil planes, apodizing in the entrance aperture plane with a special
mask), and reducing the random and systematic errors are noted. An acceptable
level of stray light in telescopes is estimated for the V-profile recording
with a signal-to-noise ratio greater than three. Prospects for the limb
chromosphere magnetic measurements are indicated.Comment: 11 pages, 3 figure
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