Optical encryption based on computational ghost imaging

Author(s): Pere Clemente, Vicente Durán, Víctor Torres-Company, Enrique Tajahuerce, Jesús Lancis

Abstract:

“Ghost imaging is an optical technique in which the information of an object is encoded in the correlation of the intensity fluctuations of light. The computational version of this fascinating phenomenon emulates, offline, the optical propagation through the reference arm, enabling 3D visualization of a complex object whose transmitted light is measured by a bucket detector. In this Letter, we show how computational ghost imaging can be used to encrypt and transmit object information to a remote party. Important features, such as key compressibility and vulnerability to eavesdropping, are experimentally analyzed.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 35, Issue 14, pp. 2391-2393 (2010)
DOI: 10.1364/OL.35.002391

Digital phase conjugation of second harmonic radiation emitted by nanoparticles in turbid media

Author(s): Chia-Lung Hsieh, Ye Pu, Rachel Grange, and Demetri Psaltis

Abstract:

“We demonstrate focusing coherent light on a nanoparticle through turbid media based on digital optical phase conjugation of second harmonic generation (SHG) field from the nanoparticle. A SHG active nanoparticle inside a turbid medium was excited at the fundamental frequency and emitted SHG field as a point source. The SHG emission was scattered by the turbid medium, and the scattered field was recorded by off-axis digital holography. A phase-conjugated beam was then generated by using a phase-only spatial light modulator and sent back through the turbid medium, which formed a nearly ideal focus on the nanoparticle.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 18, Issue 12, pp. 12283-12290 (2010)
DOI: 10.1364/OE.18.012283

Direct creation of a photoinduced metallic structure and its optical properties in the terahertz frequency region

Author(s): Takanori Okada, Kazufumi Ooi, Yosuke Nakata, Koji Fujita, Katsuhisa Tanaka, Koichiro Tanaka

Abstract:

“We investigate the surface electromagnetic characteristics of a photoinduced periodical structure using the attenuated total reflection (ATR) technique in the terahertz frequency region. A wire grating structure is generated at the surface of a silicon prism by irradiation with a spatially modulated, ultrafast pulsed laser. A characteristic minimum due to the excitation of surface waves is observed in the ATR spectrum. The depth profile of the photoinduced carrier layer is also studied. We confirm that the photoinduced structure has metallic properties. This fabrication technique will be developed as a simple method to create “active” structures.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 35, Issue 10, pp. 1719-1721 (2010)
DOI: 10.1364/OL.35.001719

Image Transmission Through an Opaque Material

Author(s): S. M. Popoff, G. Lerosey, M. Fink, A.C. Boccara, S. Gigan

Abstract:

“Optical imaging relies on the ability to illuminate an object and to collect and make sense of the light it scatters or transmit. Propagation through complex media such as biological tissues was so far believed to degrade the attainable depth as well as the resolution for imaging cite{sebbah2001introduction} because of multiple scattering. This is why such media are usually considered opaque. Recent experiments have demonstrated that multiply scattered light can in fact be harnessed thanks to wavefront control, and even put to profit to surpass what one can achieve within a homogenous medium in terms of focusing. Very recently, we have proven that it is possible to measure the complex mesoscopic optical transmission channels that allow light to traverse through an opaque medium. Here we show that we can optimally exploit those channels to coherently transmit and recover with a high fidelity an arbitrary image, independently of the complexity of the propagation. Our approach gives a general framework for coherent imaging in complex media, going well beyond focusing. It is valid for any linear complex media, and could be extended to several novel photonic materials, whatever the amount of scattering or disorder (from complete disorder to weakly disordered photonic crystals, and from superdiffusive to Anderson localization). ”

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Publication:arXiv.org / physics
Issue/Year:arXiv:1005.0532 (May 2010)

Measuring the Transmission Matrix in Optics: An Approach to the Study and Control of Light Propagation in Disordered Media

Author(s): S. M. Popoff, G. Lerosey, R. Carminati, M. Fink, A. C. Boccara, S. Gigan

Abstract:

“We introduce a method to experimentally measure the monochromatic transmission matrix of a complex medium in optics. This method is based on a spatial phase modulator together with a full-field interferometric measurement on a camera. We determine the transmission matrix of a thick random scattering sample. We show that this matrix exhibits statistical properties in good agreement with random matrix theory and allows light focusing and imaging through the random medium. This method might give important insight into the mesoscopic properties of a complex medium.”

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Publication: Physical Review Letters
Issue/Year: Phys. Rev. Lett., Volume 104, Issue 10, 100601 (2010)
DOI: 10.1103/PhysRevLett.104.100601

Individually controlled multi-focus laser processing for two-photon polymerization

Author(s): Kotaro Obata, Jürgen Koch, and Boris N. Chichkov

Abstract:

“A parallel processing of two-photon polymerization structuring is demonstrated with spatial light modulator. Spatial light modulator generates multi-focus spots on the sample surface via phase modulation technique controlled by computer generated hologram pattern. Each focus spot can be individually controlled in position and laser intensity with computer generated hologram pattern displayed on spatial light modulator. The multi-focus spots two-photon polymerization achieves the fabrication of asymmetric structure. Moreover, smooth sine curved polymerized line with amplitude of 5 μm and a period of 200 μm was obtained by fast switching of CGH pattern.”

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Publication: SPIE Proceedings / Volume 7584 / Nonlinear Processing
Issue/Year: Proc. SPIE 7584, 75840L (2010)
DOI: 10.1117/12.842117

Nonspherical laser-induced cavitation bubbles

Author(s): Kang Yuan Lim, Pedro A. Quinto-Su, Evert Klaseboer, Boo Cheong Khoo, Vasan Venugopalan, Claus-Dieter Ohl

Abstract:

“The generation of arbitrarily shaped nonspherical laser-induced cavitation bubbles is demonstrated with a optical technique. The nonspherical bubbles are formed using laser intensity patterns shaped by a spatial light modulator using linear absorption inside a liquid gap with a thickness of 40 μm. In particular we demonstrate the dynamics of elliptic, toroidal, square, and V-shaped bubbles. The bubble dynamics is recorded with a high-speed camera at framing rates of up to 300 000 frames per second. The observed bubble evolution is compared to predictions from an axisymmetric boundary element simulation which provides good qualitative agreement. Interesting dynamic features that are observed in both the experiment and simulation include the inversion of the major and minor axis for elliptical bubbles, the rotation of the shape for square bubbles, and the formation of a unidirectional jet for V-shaped bubbles. Further we demonstrate that specific bubble shapes can either be formed directly through the intensity distribution of a single laser focus, or indirectly using secondary bubbles that either confine the central bubble or coalesce with the main bubble. The former approach provides the ability to generate in principle any complex bubble geometry.”

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Publication: Physical Review E
Issue/Year: Phys. Rev. E, Volume 81, Issue 1, 016308 (2010)
DOI: 10.1103/PhysRevE.81.016308

Generating superpositions of higher–order Bessel beams

Author(s): Ruslan Vasilyeu, Angela Dudley, Nikolai Khilo, Andrew Forbes

Abstract:

“We report the first experimental generation of the superposition of higher-order Bessel beams, by means of a spatial light modulator (SLM) and a ring slit aperture. We present illuminating a ring slit aperture with light which has an azimuthal phase dependence, such that the field produced is a superposition of two or more higher-order Bessel beams. The experimentally produced fields are in good agreement with those calculated theoretically. The significance of these fields is that even though one is able to generate fields which carry zero orbital angular momentum, a rotation in the field’s intensity profile as it propagates is observed.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 17, Issue 26, pp. 23389-23395 (2009)
DOI: 10.1364/OE.17.023389

Programmable ultrashort-pulsed flying images

Author(s): M. Bock, S. K. Das, and R. Grunwald

Abstract:

“We report the generation of programmable two-dimensional arrangements of ultrashort-pulsed fringe-less Bessel-like beams of extended depth of focus (referred to as needle beams) without truncating apertures. A sub-20-fs Ti:sapphire laser and a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM) of high-fidelity temporal transfer in phase-only operation mode were used in the experiments. Axicon profiles with ultrasmall conical angles were approximated by adapted gray scale distributions. It was demonstrated that digitized image information encoded in amplitudephase maps of the needle beams is propagated over considerably large distances at minimal cross talk without the need for additional relay optics. This experiment represents a physical realization of Saari’s proposal of spatio-temporally nondiffracting “flying images” on a few-femtosecond time scale. ”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 17, Issue 9, pp. 7465-7478
DOI: 10.1364/OE.17.007465

Fast parallel diffractive multi-beam femtosecond laser surface micro-structuring

Author(s): Zheng Kuang, Dun Liu, Walter Perrie, Stuart Edwardson, Martin Sharp, Eamonn Fearon, Geoff Dearden, Ken Watkins

Abstract:

“Fast parallel femtosecond laser surface micro-structuring is demonstrated using a spatial light modulator (SLM). The Gratings and Lenses algorithm, which is simple and computationally fast, is used to calculate computer generated holograms (CGHs) producing diffractive multiple beams for the parallel processing. The results show that the finite laser bandwidth can significantly alter the intensity distribution of diffracted beams at higher angles resulting in elongated hole shapes. In addition, by synchronisation of applied CGHs and the scanning system, true 3D micro-structures are created on Ti6Al4V.”

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Publication: Applied Surface Science
Issue/Year: Applied Surface Science, Volume 255, Issues 13-14, 15 April 2009, Pages 6582-6588
DOI: 10.1016/j.apsusc.2009.02.043