Article

# Focusing coherent light through opaque strongly scattering media

Complex Photonic Systems, Faculty of Science and Technology and MESA+ Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
(Impact Factor: 3.29). 09/2007; 32(16):2309-11. DOI: 10.1364/OL.32.002309
Source: PubMed

ABSTRACT

We report focusing of coherent light through opaque scattering materials by control of the incident wavefront. The multiply scattered light forms a focus with a brightness that is up to a factor of 1000 higher than the brightness of the normal diffuse transmission.

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• "In short, the process starts with a single input mode k incident on the scattering medium. We optimize the output mode m by fitting the optimal phase for each SLM segment that results in maximum constructive interference in the multimode fiber [4], using direct (classical) light from the laser. Each input mode is controlled by approximately 960 segments on the SLM. "
##### Article: Programmable two-photon quantum interference in $10^3$ channels in opaque scattering media
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ABSTRACT: We investigate two-photon quantum interference in an opaque scattering medium that intrinsically supports $10^6$ transmission channels. By adaptive spatial phase-modulation of the incident wavefronts, the photons are directed at targeted speckle spots or output channels. From $10^3$ experimentally available coupled channels, we select two channels and enhance their transmission, to realize the equivalent of a fully programmable $2\times2$ beam splitter. By sending pairs of single photons from a parametric down-conversion source through the opaque scattering medium, we observe two-photon quantum interference. The programmed beam splitter need not fulfill energy conservation over the two selected output channels and hence could be non-unitary. Consequently, we have the freedom to tune the quantum interference from bunching (Hong-Ou-Mandel-like) to antibunching. Our results establish opaque scattering media as a platform for high-dimensional quantum interference that is notably relevant for boson sampling and physical-key-based authentication.
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• "In scattering medium the energy of the initial beam is not lost but is instead converted into a diffuse glow of scattered light. This diffusively scattered light makes objects look blurred and thus represents a major obstacle to the imaging and focusing of light in different fields such as biomedical imaging, laser therapy, oceanology [1] [2]. "
##### Conference Paper: Laser beam propagation and wavefront correction in turbid media
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ABSTRACT: It is well known that turbid medium such as fog or biological tissues causes light scatter. This phenomenon is known as major impediment for imaging and focusing of light. Thus it is important to understand the impact of the turbid medium on the light characteristics, namely intensity and phase distributions. In this work laser beam propagation through the scattering suspension of polystyrene microspheres in distilled water was investigated both theoretically and experimentally. We obtained the dependence of the wavefront aberrations on the particles concentration and shown the existence of high-order symmetric wavefront aberrations of the laser beam passed through turbid medium. The investigation showed that with the use of bimorph deformable mirror the wavefront aberrations of scattered light could be effectively corrected.
SPIE Unconventional Imaging and Wavefront Sensing 2015; 09/2015
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• "In 1990 Freund predicted that precise optical devices could be made using opaque media and wavefront shaping [1]. Since then this technique has been used to control: transmission through opaque materials [2], the polarization of light [3] [4], broadband spectral characteristics [5] [6] [7] [8], and the spatio-spectral properties of random lasers [9] [10] [11] [12]. It has also been used to enhance fluorescence microscopy [13] [14], achieve perfect focusing [13] [15], compress ultrashort pulses [16] [17] and enhance astronomical and biological imaging [18] [19]. "
##### Article: Stability of optimal-wave-front-sample coupling under sample translation and rotation
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ABSTRACT: The method of wavefront shaping to control optical properties of opaque media is a promising technique for authentication applications. One of the main challenges of this technique is the sensitivity of the wavefront-sample coupling to translation and/or rotation. To better understand how translation and rotation affect the wavefront- sample coupling we perform experiments in which we first optimize reflection from an opaque surface—to obtain an optimal wavefront—and then translate or rotate the surface and measure the new reflected intensity pattern. By using the correlation between the optimized and translated or rotated patterns we determine how sensitive the wavefront-sample coupling is. These experiments are performed for different spatial-light-modulator (SLM) bin sizes, beam-spot sizes, and nanoparticle concentrations. We find that all three parameters affect the different positional changes, implying that an optimization scheme can be used to maximize the stability of the wavefront-sample coupling. We also develop a model to simulate sample translation or rotation and its effect on the coupling stability, with the simulation results being qualitatively consistent with experiment.
Physical Review A 06/2015; 91(6):063802. DOI:10.1103/PhysRevA.91.063802 · 2.81 Impact Factor