126 research outputs found
Correlations between reflected and transmitted intensity patterns emerging from opaque disordered media
The propagation of monochromatic light through a scattering medium produces
speckle patterns in reflection and transmission, and the apparent randomness of
these patterns prevents direct imaging through thick turbid media. Yet, since
elastic multiple scattering is fundamentally a linear and deterministic
process, information is not lost but distributed among many degrees of freedom
that can be resolved and manipulated. Here we demonstrate experimentally that
the reflected and transmitted speckle patterns are correlated, even for opaque
media with thickness much larger than the transport mean free path, proving
that information survives the multiple scattering process and can be recovered.
The existence of mutual information between the two sides of a scattering
medium opens up new possibilities for the control of transmitted light without
any feedback from the target side, but using only information gathered from the
reflected speckle.Comment: 6 pages, 4 figure
Absorption imaging of a quasi 2D gas: a multiple scattering analysis
Absorption imaging with quasi-resonant laser light is a commonly used
technique to probe ultra-cold atomic gases in various geometries. Here we
investigate some non-trivial aspects of this method when it is applied to in
situ diagnosis of a quasi two-dimensional gas. Using Monte Carlo simulations we
study the modification of the absorption cross-section of a photon when it
undergoes multiple scattering in the gas. We determine the variations of the
optical density with various parameters, such as the detuning of the light from
the atomic resonance and the thickness of the gas. We compare our results to
the known three-dimensional result (Beer-Lambert law) and outline the specific
features of the two-dimensional case.Comment: 22 pages, 5 figure
Scattering invariant modes of light in complex media
Random scattering of light in disordered media is an intriguing phenomenon of
fundamental relevance to various applications. While techniques such as
wavefront shaping and transmission matrix measurements have enabled remarkable
progress for advanced imaging concepts, the most successful strategy to obtain
clear images through a disordered medium remains the filtering of ballistic
light. Ballistic photons with a scattering-free propagation are, however,
exponentially rare and no method so far can increase their proportion. To
address these limitations, we introduce and experimentally implement here a new
set of optical states that we term Scattering Invariant Modes (SIMs), whose
transmitted field pattern is the same, irrespective of whether they scatter
through a disordered sample or propagate ballistically through a homogeneous
medium. We observe SIMs that are only weakly attenuated in dense scattering
media, and show in simulations that their correlations with the ballistic light
can be used to improve imaging inside scattering materials
Wavefront shaping with disorder-engineered metasurfaces
Recently, wavefront shaping with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics, including extended volume, aberration-free focusing and subwavelength focusing. However, translating these capabilities to useful applications has remained challenging as the input–output characteristics of the disordered media (P variables) need to be exhaustively determined via O(P) measurements. Here, we propose a paradigm shift where the disorder is specifically designed so its exact input–output characteristics are known a priori and can be used with only a few alignment steps. We implement this concept with a disorder-engineered metasurface, which exhibits additional unique features for wavefront shaping such as a large optical memory effect range in combination with a wide angular scattering range, excellent stability, and a tailorable angular scattering profile. Using this designed metasurface with wavefront shaping, we demonstrate high numerical aperture (NA > 0.5) focusing and fluorescence imaging with an estimated ~2.2 × 10^8 addressable points in an ~8 mm field of view
La politique de l'emploi face aux nouveaux modes de gouvernance axés sur la coordination et la performance
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