330 research outputs found
Manipulating the transmission matrix of scattering media for nonlinear imaging beyond the memory effect
The measurement of the Transmission Matrix (TM) of a scattering medium is of
great interest for imaging. It can be acquired directly by interferometry using
an internal reference wavefront. Unfortunately, internal reference fields are
scattered by the medium which results in a speckle that makes the TM
measurement heterogeneous across the output field of view. We demonstrate how
to correct for this effect using the intrinsic properties of the TM. For thin
scattering media, we exploit the memory effect of the medium and the reference
speckle to create a corrected TM. For highly scattering media where the memory
effect is negligible, we use complementary reference speckles to compose a new
TM, not compromised by the speckled reference anymore. Using this correction,
we demonstrate large field of view second harmonic generation imaging through
thick biological media
Enhanced nonlinear imaging through scattering media using transmission matrix based wavefront shaping
Despite the tremendous progresses in wavefront control through or inside
complex scattering media, several limitations prevent reaching practical
feasibility for nonlinear imaging in biological tissues. While the optimization
of nonlinear signals might suffer from low signal to noise conditions and from
possible artifacts at large penetration depths, it has nevertheless been
largely used in the multiple scattering regime since it provides a guide star
mechanism as well as an intrinsic compensation for spatiotemporal distortions.
Here, we demonstrate the benefit of Transmission Matrix (TM) based approaches
under broadband illumination conditions, to perform nonlinear imaging. Using
ultrashort pulse illumination with spectral bandwidth comparable but still
lower than the spectral width of the scattering medium, we show strong
nonlinear enhancements of several orders of magnitude, through thicknesses of a
few transport mean free paths, which corresponds to millimeters in biological
tissues. Linear TM refocusing is moreover compatible with fast scanning
nonlinear imaging and potentially with acoustic based methods, which paves the
way for nonlinear microscopy deep inside scattering media
Filtering of matter symmetry properties by circularly polarized nonlinear optics
International audienceWe propose a direct readout of symmetry information in matter using nonlinear optics. From combinations of circularly and longitudinally polarized optical fields, we construct irreducible spherical field tensors for second- and third-order nonlinear processes. The coupling of these field tensors to the matter susceptibility tensors allows filtering out of the susceptibility symmetries independently of the sample orientation in the laboratory frame. Experimental demonstrations are conducted on microcrystals, in a microscopy configuration compatible with symmetry order imaging
Quantitative analysis of light scattering in polarization-resolved nonlinear microscopy
International audiencePolarization resolved nonlinear microscopy (PRNM) is a powerful technique to gain microscopic structural information in biological media. However, deep imaging in a variety of biological specimens is hindered by light scattering phenomena, which not only degrades the image quality but also affects the polarization state purity. In order to quantify this phenomenon and give a framework for polarization resolved microscopy in thick scattering tissues, we develop a characterization methodology based on four wave mixing (FWM) process. More specifically, we take advantage of two unique features of FWM, meaning its ability to produce an intrinsic in-depth local coherent source and its capacity to quantify the presence of light depolarization in isotropic regions inside a sample. By exploring diverse experimental layouts in phantoms with different scattering properties, we study systematically the influence of scattering on the nonlinear excitation and emission processes. The results show that depolarization mechanisms for the nonlinearly generated photons are highly dependent on the scattering center size, the geometry used (epi/forward) and, most importantly, on the thickness of the sample. We show that the use of an un-analyzed detection makes the polarization-dependence read-out highly robust to scattering effects, even in regimes where imaging might be degraded. The effects are illustrated in polarization resolved imaging of myelin lipid organization in mouse spinal cord
Wide field fluorescence epi-microscopy behind a scattering medium enabled by speckle correlations
Fluorescence microscopy is widely used in biological imaging, however
scattering from tissues strongly limits its applicability to a shallow depth.
In this work we adapt a methodology inspired from stellar speckle
interferometry, and exploit the optical memory effect to enable fluorescence
microscopy through a turbid layer. We demonstrate efficient reconstruction of
micrometer-size fluorescent objects behind a scattering medium in
epi-microscopy, and study the specificities of this imaging modality
(magnification, field of view, resolution) as compared to traditional
microscopy. Using a modified phase retrieval algorithm to reconstruct
fluorescent objects from speckle images, we demonstrate robust reconstructions
even in relatively low signal to noise conditions. This modality is
particularly appropriate for imaging in biological media, which are known to
exhibit relatively large optical memory ranges compatible with tens of
micrometers size field of views, and large spectral bandwidths compatible with
emission fluorescence spectra of tens of nanometers widths
Coherent anti-Stokes Raman scattering through thick biological tissues by single wavefront shaping
Coherent Anti Stokes Raman Scattering (CARS) offers many advantages for
nonlinear bio-imaging, thanks to its sub-cellular spatial resolution and unique
chemical specificity. Its working principle requires two incident pulsed laser
beams with distinct frequencies to be focused in space and time, which focus
quality however rapidly deteriorates when propagating at large depths in
biological tissues. The depth limits of CARS and the capability of wavefront
correction to overcome these limits are currently unknown. In this work we
exploit the spectral correlation properties of the transmission matrix of a
scattering medium in a pulsed regime, to recover coherent focusing for two
distant incident CARS wavelengths which propagation is initially uncorrelated.
Using wavefront shaping with a single spatial light modulator, we recover CARS
generation through thick mice spinal cord tissues where initially no signal is
measurable due to scattering, and demonstrate point scanning over large field
of views of tens of micrometers.Comment: 25 pages, 7 figure
Periodic skyrmionic textures via conformal cartographic projections
We find periodic skyrmionic textures via conformal cartographic projections
that map either an entire spherical parameter space or a hemisphere onto every
regular polygon that provides regular tessellations of the plane. These maps
preserve the sign of the Skyrme density throughout the entire space. We
implement these textures in the polarization state of a laser beam, and
demonstrate that paraxial fields where a periodic texture preserving the sign
of the Skyrme density is implemented in the polarization state distribution
unavoidably exhibit zeros
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