145 research outputs found
Increasing the imaging capabilities of multimode fibers by exploiting the properties of highly scattering media
We present a novel design that exploits the focusing properties of scattering
media to increase the resolution and the working distance of multimode fiber
based imaging devices. Placing a highly scattering medium in front of the
distal tip of the multimode fiber enables the formation of smaller sized foci
at increased working distances away from the fiber tip. We perform a parametric
study of the effect of the working distance and the separation between the
fiber and the scattering medium on the focus size. We experimentally
demonstrate submicron focused spots as far away as 800{\mu}m with 532nm light.Comment: 4 pages, 3 figure
A Learning Approach to Optical Tomography
We describe a method for imaging 3D objects in a tomographic configuration
implemented by training an artificial neural network to reproduce the complex
amplitude of the experimentally measured scattered light. The network is
designed such that the voxel values of the refractive index of the 3D object
are the variables that are adapted during the training process. We demonstrate
the method experimentally by forming images of the 3D refractive index
distribution of cells
Delivery of focused short pulses through a multimode fiber
Light propagation through multimode fibers suffers from spatial distortions
that lead to a scrambled intensity profile. In previous work, the correction of
such distortions using various wavefront control methods has been demonstrated
in the continuous wave case. However, in the ultra-fast pulse regime, modal
dispersion temporally broadens a pulse after propagation. Here, we present a
method that compensates for spatial distortions and mitigates temporal
broadening due to modal dispersion by a selective phase conjugation process in
which only modes of similar group velocities are excited. The selectively
excited modes are forced to follow certain paths through the multimode fiber
and interfere constructively at the distal tip to form a focused spot with
minimal temporal broadening. We demonstrate the delivery of focused 500 fs
pulses through a 30 cm long step-index multimode fiber. The achieved pulse
duration corresponds to approximately 1/30th of the duration obtained if modal
dispersion was not controlled. Moreover, we measured a detailed two-dimensional
map of the pulse duration at the output of the fiber and confirmed that the
focused spot produces a two-photon absorption effect. This work opens new
possibilities for ultra-thin multiphoton imaging through multimode fibers
Dynamic conjugate F-SHARP microscopy
Optical microscopy is an indispensable tool in biomedical sciences, but its reach in deep tissues is limited due to aberrations and scattering. This problem can be overcome by wavefront-shaping techniques, albeit at limited fields of view (FOVs). Inspired by astronomical imaging, conjugate wavefront shaping can lead to an increased field of view in microscopy, but this correction is limited to a set depth and cannot be dynamically adapted. Here, we present a conjugate wavefront-shaping scheme based on focus scanning holographic aberration probing (F-SHARP). We combine it with a compact implementation that can be readily adapted to a variety of commercial and home-built two-photon microscopes. We demonstrate the power of the method by imaging with high resolution over extended FOV (>80 µm) deeper than 400 μm inside a mouse brain through a thinned skull
Translation correlations in anisotropically scattering media
Controlling light propagation across scattering media by wavefront shaping
holds great promise for a wide range of communications and imaging
applications. However, finding the right wavefront to shape is a challenge when
the mapping between input and output scattered wavefronts (i.e. the
transmission matrix) is not known. Correlations in transmission matrices,
especially the so-called memory-effect, have been exploited to address this
limitation. However, the traditional memory-effect applies to thin scattering
layers at a distance from the target, which precludes its use within thick
scattering media, such as fog and biological tissue. Here, we theoretically
predict and experimentally verify new transmission matrix correlations within
thick anisotropically scattering media, with important implications for
biomedical imaging and adaptive optics.Comment: main article (18 pages) and appendices (6 pages
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