Frequency bandwidth of light focused through turbid media

Author(s): Frerik van Beijnum, Elbert G. van Putten, Ad Lagendijk, and Allard P. Mosk

Abstract:

“We study the effect of frequency detuning on light focused through turbid media. By shaping the wavefront of the incident beam light is focused through an opaque scattering layer. When detuning the laser we observe a gradual decrease of the focus intensity, while the position, size,and shape of the focus remain the same within experimental accuracy. The frequency dependence of the focus intensity follows a measured speckle correlation function. We support our experimental findings with calculations based on transport theory. Our results imply wavefront shaping methods can be generalized to allow focusing of optical pulses in turbid media.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 36, Issue 3, pp. 373-375 (2011)
doi:10.1364/OL.36.000373

Constructing petal modes from the coherent superposition of Laguerre-Gaussian modes

Author(s): Darryl Naidoo, Andrew Forbes, Kamel Ait-Ameur, Marc Brunel

Abstract:

“An experimental approach in generating Petal-like transverse modes, which are similar to what is seen in porro-prism resonators, has been successfully demonstrated. We hypothesize that the petal-like structures are generated from a coherent superposition of Laguerre-Gaussian modes of zero radial order and opposite azimuthal order. To verify this hypothesis, visually based comparisons such as petal peak to peak diameter and the angle between adjacent petals are drawn between experimental data and simulated data. The beam quality factor of the Petal-like transverse modes and an inner product interaction is also experimentally compared to numerical results.”

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Publication: SPIE Proceedings, (subscription required)

Issue/Year/DOI: Proc. SPIE 7913, 791304 (2011)
doi:10.1117/12.876854

Dynamic space shaping of intense ultrashort laser light with blazed-type gratings

Author(s): I. Marienko, V. Denisenko, V Slusar, and M. Soskin

Abstract:

“A beam shaper for dynamic transversal shaping of broadband laser pulses that utilizes a blazed ruled grating and a blazed-type grating simulated on Spatial Light Modulator was demonstrated. The introduced shaper scheme is an extension of 2f-2f scheme [Mariyenko, et al., Opt. Express 13, 7599 (2005)] where the two thin holograms with matched grating constants performed light shaping. The new scheme utilizes the diffraction gratings with different grating constants. Dispersion-free light shaping is achieved by means of the intermediate transversal light beam magnification. The magnification balances the mismatch in the grating constants resulting in total residual angular dispersion compensation. In turn, the magnified beam covers a greater area on the modulator matrix thus reducing the incident light power density by a value equal to square of the magnification factor. It translates to the safe-operation threshold extension of the modulator allowing shaping pulses that are powerful enough to be used in the applications. With a proper components selection, the throughput efficiency of the shaper can be well above 40%. A proper shaper operation was demonstrated with the 140-fs Ti:Sapphire oscillator. Theoretical calculations support the conclusions.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 18, Issue 24, pp. 25143-25150 (2010)
doi:10.1364/OE.18.025143

Increasing multimode fiber transmission capacity by mode selective spatial light phase modulation

Author(s): Stepniak, G.; Maksymiuk, L.; Siuzdak, J.;

Abstract:

“We propose spatial light modulation with binary phase filters to increase the transmission bandwidth of multimode fibers. In the experiment more than 300 % of bandwidth enhancement is obtained.”

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Publication: ECOC Proceedings, (subscription required)

Issue/Year/DOI: 36th European Conference and Exhibition on Optical Communication (ECOC), 2010
doi:10.1109/ECOC.2010.5621465

Imaging through turbid layers by scanning the phase conjugated second harmonic radiation from a nanoparticle

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

Abstract:

“We demonstrate imaging through a turbid layer by using digital phase conjugation of the second harmonic field radiated from a beacon nanoparticle. We show that the phase-conjugated focus can be displaced from its initial position by illuminating the same region of the turbid layer with an angular offset. An image is obtained by scanning the phase-conjugated focus through the turbid layer in a region around the nanoparticle. We obtain a clear image of the target by measuring the light transmitted through it when scanning the focused beam.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 18, Issue 20, pp. 20723-20731 (2010)
doi:10.1364/OE.18.020723

Application of cooled spatial light modulator for high power nanosecond laser micromachining

Author(s): Rainer J. Beck, Jonathan P. Parry, William N. MacPherson, Andrew Waddie, Nick J. Weston, Jonathan D. Shephard, and Duncan P. Hand

Abstract:

“The application of a commercially available spatial light modulator (SLM) to control the spatial intensity distribution of a nanosecond pulsed laser for micromachining is described for the first time. Heat sinking is introduced to increase the average power handling capabilities of the SLM beyond recommended limits by the manufacturer. Complex intensity patterns are generated, using the Inverse Fourier Transform Algorithm, and example laser machining is demonstrated. The SLM enables both complex beam shaping and also beam steering.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 18, Issue 16, pp. 17059-17065 (2010)
doi:10.1364/OE.18.017059

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 (subscription required)

Issue/Year/DOI: 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, (free download)

Issue/Year/DOI: 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 (subscription required)

Issue/Year/DOI: 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 (free download)

Issue/Year/DOI: arXiv:1005.0532 (May 2010)