Eigenmodes of a hydrodynamically coupled micron-size multiple-particle ring

Author(s): R. Di Leonardo, S. Keen, J. Leach, C. D. Saunter, G. D. Love, G. Ruocco and M. J. Padgett

Abstract:

“We use a continuous acquisition, high-speed camera with integrated centroid tracking to simultaneously measure the positions of a ring of micron-sized particles held in holographic optical tweezers. Hydrodynamic coupling between the particles gives a set of eigenmodes, each one independently relaxing with a characteristic decay rate (eigenvalue) that can be measured using our positional data. Despite the finite particle size, we find an excellent agreement between the measured eigenvalues and those numerically predicted by Oseen theory applied to the two-dimensional (2D) ring geometry. Particle motions are also analyzed in terms of the alternative eigenmode set obtained by wrapping onto the ring the eigenmodes of a 1D periodic chain. We identify the modes for which the periodic chain is a good approximation to the ring and those for which it is not.”

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Publication: Physical Review E
Issue/Year: Phys. Rev. E 76, Issue 6, 061402 (2007)
DOI: 10.1103/PhysRevE.76.061402

Wavelength-multiplexed submicron holograms for disk-compatible data storage

Author(s): Pengfei Wu, Zhiqiang Liu, Jame J. Yang, Angel Flores, and Michael R. Wang

Abstract:

“By using a hybrid diffractive and refractive achromat with extended depth of focus, we have successfully recorded a micro-hologram array with diffraction-limited individual spot size maintained throughout the thickness of recording medium. An electrically programmable wavelength combiner was constructed in which a white light source was adopted. By modifying on a commercial CD readout head, we configured a compact micro-hologram recording/readout system that is compatible to existing disk storage technology. Base on the wavelength combiner and recording/readout system, wavelength-multiplexed micro-holograms were recorded and recovered. The presented results demonstrate the practicality of our novel storage architecture.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 15, Issue 26, pp. 17798-17804
DOI: 10.1364/OE.15.017798

Electrostatic Interactions of Colloidal Particles in Nonpolar Solvents: Role of Surface Chemistry and Charge Control Agents

Author(s): Sunil K. Sainis, Vincent Germain, Cecile O. Mejean, and Eric R. Dufresne

Abstract:

“We study the electrostatic and hydrodynamic interactions of colloidal particles in nonpolar solvents. Using blinking optical tweezers, we can extract the screening length, K-1, the effective surface potential, |eζ*|, and the hydrodynamic radius, ah, in a single measurement. We apply this technique to suspensions of polystyrene and poly(methyl methacrylate) particles in hexadecane with soluble charge control agents, aerosol sodium di-2-ethylhexylsulfosuccinate (AOT) and polyisobutylene succinimide (OLOA-1200). We find that the electrostatic interactions of these particles depend sensitively on surface composition as well as on the concentration and chemistry of the charge control agent.”

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Publication: Langmuir
Issue/Year: Langmuir, 2008, 24 (4), pp 1160–1164
DOI: 10.1021/la702432u

Phase and amplitude pulse shaping with two-dimensional phase-only spatial light modulators

Author(s): Eugene Frumker and Yaron Silberberg

Abstract:

“We consider a programmable, phase, and amplitude femtosecond pulse shaper based on a two-dimensional (2D) reflective liquid-crystal (LC) spatial light modulator (SLM). A new zero-order pulse shaping scheme is introduced and compared to the first-order scheme, both theoretically and experimentally, using liquid crystal on silicon 2D SLM. While the spectral components of the pulse are spread across the horizontal dimension, we use the vertical direction for modulation of both spectral phases and amplitudes. It was found that while zero-order approach provided better light efficiency (67% versus 43%), the first-order scheme has superior dynamic range of amplitude modulation.”

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Publication: Journal of the Optical Society of America B
Issue/Year: JOSA B, Vol. 24, Issue 12, pp. 2940-2947
DOI: 10.1364/JOSAB.24.002940

Parallel photopolymerisation with complex light patterns generated by diffractive optical elements

Author(s): Lóránd Kelemen, Sándor Valkai, and Pál Ormos

Abstract:

“Photopolymerisation by scanning a focused laser beam is a powerful method to build structures of arbitrary complexity with submicrometer resolution. We introduce parallel photopolymerisation to enhance the efficiency. Instead of multidimensional scanning of a single focus, the structure is generated simultaneously with diffractive patterns. We used fixed diffractive optical elements (DOEs), kinoforms, and Spatial Light Modulators (SLMs). The possibilities of photopolymerisation using SLM were investigated: the added flexibility using the programmable device is demonstrated. By using these DOEs, straight and helical cross shaped columns were produced with a single scan at a rate about an order of magnitude faster than by simple scanning. The produced helical structures could be rotated by optical tweezers.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 15, Issue 22, pp. 14488-14497 (2007)
DOI: 10.1364/OE.15.014488

Parallel photopolymerisation with complex light patterns generated by diffractive optical elements

Author(s): Lóránd Kelemen, Sándor Valkai, and Pál Ormos

Abstract:

“Photopolymerisation by scanning a focused laser beam is a powerful method to build structures of arbitrary complexity with submicrometer resolution. We introduce parallel photopolymerisation to enhance the efficiency. Instead of multidimensional scanning of a single focus, the structure is generated simultaneously with diffractive patterns. We used fixed diffractive optical elements (DOEs), kinoforms, and Spatial Light Modulators (SLMs). The possibilities of photopolymerisation using SLM were investigated: the added flexibility using the programmable device is demonstrated. By using these DOEs, straight and helical cross shaped columns were produced with a single scan at a rate about an order of magnitude faster than by simple scanning. The produced helical structures could be rotated by optical tweezers.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 15, Issue 22, pp. 14488-14497 (2007)
DOI: 10.1364/OE.15.014488

Hypergeometric-Gaussian modes

Author(s): Ebrahim Karimi, Gianluigi Zito, Bruno Piccirillo, Lorenzo Marrucci, and Enrico Santamato

Abstract:

“We studied a novel family of paraxial laser beams forming an overcomplete yet nonorthogonal set of modes. These modes have a singular phase profile and are eigenfunctions of the photon orbital angular momentum. The intensity profile is characterized by a single brilliant ring with the singularity at its center, where the field amplitude vanishes. The complex amplitude is proportional to the degenerate (confluent) hypergeometric function, and therefore we term such beams hypergeometric-Gaussian (HyGG) modes. Unlike the recently introduced hypergeometric modes [Opt. Lett. 32, 742 (2007)], the HyGG modes carry a finite power and have been generated in this work with a liquid-crystal spatial light modulator. We briefly consider some subfamilies of the HyGG modes as the modified Bessel Gaussian modes, the modified exponential Gaussian modes, and the modified Laguerre-Gaussian modes.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 32, Issue 21, pp. 3053-3055
DOI: 10.1364/OL.32.003053

The dark spots of Arago

Author(s): Pascal Fischer, Susan E. Skelton, Christopher G. Leburn, Casey T. Streuber, Ewan M. Wright, and Kishan Dholakia

Abstract:

“We explore the diffraction and propagation of Laguerre- Gaussian beams of varying azimuthal index past a circular obstacle both experimentally and numerically. When the beam and obstacle centers are aligned the famous spot of Arago, which arises for zero azimuthal index, is replaced for non-zero azimuthal indices by a dark spot of Arago, a simple consequence of the conserved phase singularity at the beam center. We explore how the dark spot of Arago behaves as the beam and obstacle centers are progressively misaligned, and find that the central dark spot may break into several dark spots of Arago for higher incident azimuthal index beams. ”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 15, Issue 19, pp. 11860-11873
DOI: 10.1364/OE.15.011860

A high-capacity storage device for communications and multimedia systems

Author(s): Z. Y. Chen, Po S. Chung

Abstract:

“This paper introduces a high-capacity storage device based on the holographic optical disc storage system and applied field. It details a novel configuration of a single beam holographic storage system. Through coding the object light and reference light in same optical beam with a spatial light modulator (SLM), we achieve the aim of interference storage. The experimental results indicated this configuration can be used commercially. This system has the advantages of huge memory capacity and high access speed, thus offering a very useful storage alternative in the internet areas of communications and multimedia systems.”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE, Vol. 6775, 67750S (2007)
DOI: 10.1117/12.730495

Focusing coherent light through opaque strongly scattering media

Author(s): I. M. Vellekoop and A. P. Mosk

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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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 32, Issue 16, pp. 2309-2311
DOI: 10.1364/OL.32.002309
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