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