[Show abstract][Hide abstract] ABSTRACT: We present a method to measure the spectrally-resolved transmission matrix of
a multiply scattering medium, thus allowing for the deterministic
spatiospectral control of a broadband light source by means of wavefront
shaping. As a demonstration, we show how the medium can be used to selectively
focus one or many spectral components of a femtosecond pulse, and how it can be
turned into a controllable dispersive optical element to spatially separate
different spectral components to arbitrary positions.
[Show abstract][Hide abstract] ABSTRACT: We present an approach for two-dimensional (2D) imaging through a single
single-mode or multimode fiber without the need for scanners. A random
scattering medium placed next to the distal end of the fiber is used to encode
the collected light from every input spatial position with a different random
spectral signature. We demonstrate 2D imaging of objects illuminated by a
white-light fiber-coupled LED from a single measured spectrum. The technique is
insensitive to fiber bending, an advantage for endoscopic applications.
[Show abstract][Hide abstract] ABSTRACT: Diffraction-limited imaging through complex scattering media is a long sought
after goal with important applications in biomedical research. In recent years,
high resolution wavefront-shaping has emerged as a powerful approach to
generate a sharp focus through highly scattering, visually opaque samples.
However, it requires a localized feedback signal from the target point of
interest, which necessitates an invasive procedure in all-optical techniques.
Here, we show that by exploiting optical nonlinearities, a diffraction-limited
focus can be formed inside or through a complex sample, even when the feedback
signal is not localized. We prove our approach theoretically and numerically,
and experimentally demonstrate it with a two-photon fluorescence signal through
highly scattering biological samples. We use the formed focus to perform
two-photon microscopy through highly scattering, visually opaque layers.
[Show abstract][Hide abstract] ABSTRACT: We implement the photoacoustic transmission matrix approach on a two-dimensional photoacoustic imaging system, using a 15 MHz linear ultrasound array. Using a black leaf skeleton as a complex absorbing structure, we demonstrate that the photoacoustic transmission matrix approach allows to reveal structural features that are invisible in conventional photoacoustic images, as well as to selectively control light focusing on absorbing targets, leading to a local enhancement of the photoacoustic signal.
[Show abstract][Hide abstract] ABSTRACT: We investigate experimentally the use of speckle illumination for photoacoustic imaging. In particular, we demonstrate that otherwise invisible features are revealed through high-frequency signals fluctuations from different speckle realizations.
[Show abstract][Hide abstract] ABSTRACT: Imaging with optical resolution through and inside complex samples is a
difficult challenge with important applications in many fields. The fundamental
problem is that inhomogeneous samples, such as biological tissues, randomly
scatter and diffuse light, impeding conventional image formation. Despite many
advancements, no current method enables to noninvasively image in real-time
using diffused light. Here, we show that owing to the memory-effect for speckle
correlations, a single image of the scattered light, captured with a standard
high-resolution camera, encodes all the information that is required to image
through the medium or around a corner. We experimentally demonstrate
single-shot imaging through scattering media and around corners using
incoherent light and various samples, from white paint to dynamic biological
samples. Our lensless technique is simple, does not require laser sources,
wavefront-shaping, nor time-gated detection, and is realized here using a
camera-phone. It has the potential to enable imaging in currently inaccessible
[Show abstract][Hide abstract] ABSTRACT: The recent theory of compressive sensing leverages upon the structure of signals to acquire them with much fewer measurements than was previously thought necessary, and certainly well below the traditional Nyquist-Shannon sampling rate. However, most implementations developed to take advantage of this framework revolve around controlling the measurements with carefully engineered material or acquisition sequences. Instead, we use the natural randomness of wave propagation through multiply scattering media as an optimal and instantaneous compressive imaging mechanism. Waves reflected from an object are detected after propagation through a well-characterized complex medium. Each local measurement thus contains global information about the object, yielding a purely analog compressive sensing method. We experimentally demonstrate the effectiveness of the proposed approach for optical imaging by using a 300-micrometer thick layer of white paint as the compressive imaging device. Scattering media are thus promising candidates for designing efficient and compact compressive imagers.
[Show abstract][Hide abstract] ABSTRACT: This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.38.005188 . Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.
In high-frequency photoacoustic imaging with uniform illumination, homogeneous photoabsorbing structures may be invisible because of their large size or limited-view issues. Here we show that, by exploiting dynamic speckle illumination, it is possible to reveal features that are normally invisible with a photoacoustic system comprised of a 20 MHz linear ultrasound array. We demonstrate imaging of a ∅5 mm absorbing cylinder and a 30 μm black thread arranged in a complex shape. The hidden structures are directly retrieved from photoacoustic images recorded for different random speckle illuminations of the phantoms by assessing the variation in the value of each pixel over the illumination patterns.
[Show abstract][Hide abstract] ABSTRACT: We experimentally and numerically study the potential of
photoacoustic-guiding for light focusing through scattering samples via
wavefront-shaping and iterative optimization. We experimentally demonstrate
that the focusing efficiency on an extended absorber can be improved by
iterative optimization of the high frequency components of the broadband
photoacoustic signal detected with a spherically focused transducer. We
demonstrate more than 8-fold increase in the photoacoustic signal generated by
a 30 microns wire using a narrow frequency band around 60MHz. We numerically
confirm that such optimization leads to a smaller optical focus than using the
low frequency content of the photoacoustic feedback.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate how to measure accurately the transmission matrix of a complex medium. With this information, we show how to focus light, recover an image, and even perform efficient reconstruction of a sparse object.
Computational Optical Sensing and Imaging; 06/2013
[Show abstract][Hide abstract] ABSTRACT: Optical wavefront-shaping has emerged as a powerful tool to manipulate light
in strongly scattering media. It enables diffraction-limited focusing and
imaging at depths where conventional microscopy techniques fail. However, while
most wavefront-shaping works to-date exploited direct access to the target or
implanted probes, the challenge is to apply it non-invasively inside complex
samples. Ultrasonic-tagging techniques have been recently demonstrated but
these require a sequential point-by- point acquisition, a major drawback for
imaging applications. Here, we introduce a novel approach to non-invasively
measure the optical transmission-matrix inside a scattering medium, exploiting
the photo-acoustic effect. Our approach allows for the first time to
simultaneously discriminate, localize, and selectively focus light on multiple
targets inside a scattering sample, as well as to recover and exploit the
scattering medium properties. Combining the powerful approach of the
transmission-matrix with the advantages of photoacoustic imaging opens the path
towards deep-tissue imaging and light-delivery utilizing endogenous optical
[Show abstract][Hide abstract] ABSTRACT: The measurement of the polychromatic transmission matrix of a multiply scattering medium is reported, thus allowing control the propagation of an ultrashort pulse through the medium. We also report on our effort towards fast transmission matrix measurement.
[Show abstract][Hide abstract] ABSTRACT: Focusing light through dynamically varying heterogeneous media is a
sought-after goal with important applications ranging from free-space
communication to nano-surgery. The underlying challenge is to control
the optical wavefront with a large number of degrees-of-freedom (DOF) at
timescales shorter than the medium dynamics. Recently, many advancements
have been reported following the demonstration of focusing through
turbid samples by wavefront-shaping, using spatial light modulators
(SLMs) having >1000 DOF. Unfortunately, SLM-based wavefront-shaping
requires feedback from a detector/camera and is limited to
slowly-varying samples. Here, we demonstrate a novel approach for
wavefront-shaping using all-optical feedback. We show that the complex
wavefront required to focus through highly scattering samples, including
thin biological tissues, can be generated at sub-microsecond timescales
by the process of field self-organization inside a multimode laser
cavity, without requiring electronic feedback or SLMs. This
wavefront-shaping mechanism is more than five orders of magnitude faster
than state-of-the-art, reaching the timescales required in many
[Show abstract][Hide abstract] ABSTRACT: We show that the polarization state of coherent light propagating through an optically thick multiple scattering medium can be controlled by wavefront shaping, that is, by controlling only the spatial phase of the incoming field with a spatial light modulator. Any polarization state of light at any spatial position behind the scattering medium can be attained with this technique. Thus, transforming the random medium to an arbitrary optical polarization component becomes possible.
[Show abstract][Hide abstract] ABSTRACT: We show that wavefront-shaping enables spatial, temporal, spectral and polarization control of light in random media. We demonstrate real-time imaging ‘around corners’ and through turbid layers and focusing of ultrashort pulses in an epi-illumination microscope.
[Show abstract][Hide abstract] ABSTRACT: A random medium can serve as a controllable arbitrary spectral filter with spectral resolution determined by the inverse of the interaction time of the light in the medium. We use wavefront shaping to implement an arbitrary spectral response at a particular point in the scattered field. We experimentally demonstrate this technique by selecting either a narrow band or dual bands with a width of 5.5 nm each.
[Show abstract][Hide abstract] ABSTRACT: Imaging with optical resolution through turbid media is a long
sought-after goal with important applications in deep tissue imaging.
Although extensively studied, this goal was considered impractical until
recently. Adaptive-optics techniques, which can correct weak
aberrations, are inadequate for turbid samples, where light is scattered
to complex speckle patterns with a number of modes greatly exceeding the
number of degrees of control. This conception changed after the
demonstration of coherent focusing through turbid media by
wavefront-shaping, using spatial light modulators. Here, we show that
wavefront-shaping enables wide-field imaging through turbid layers with
incoherent illumination, and imaging of occluded objects using light
scattered from diffuse walls. In contrast to the recently introduced
schemes for imaging through turbid media, our technique does not require
coherent sources, interferometric detection, raster-scanning or off-line
reconstruction. Our results bring wavefront-shaping closer to practical
applications and realize the vision of looking through `walls' and
[Show abstract][Hide abstract] ABSTRACT: We analyze the spatiotemporal distortions of an ultrashort pulse focused through a thin scattering surface. We show and experimentally verify that in such a scenario temporal distortions are proportional to the distance from the optical axis and are present only outside the focal point, as result of geometrical path length differences. We use wavefront shaping to correct for the spatiotemporal distortions and to temporally compress chirped input pulses through the scattering medium.