Collisions of Dark Solitons in Elongated Bose-Einstein Condensates

Author(s): S. Stellmer, C. Becker, P. Soltan-Panahi, E.-M. Richter, S. Dörscher, M. Baumert, J. Kronjäger, K. Bongs, and K. Sengstock

Abstract:

“We present experimental data showing the head-on collision of dark solitons generated in an elongated Bose-Einstein condensate. No discernable interaction can be recorded, in full agreement with the fundamental theoretical concepts of solitons as mutually transparent quasiparticles. Our soliton generation technique allows for the creation of solitons with different depths; hence, they can be distinguished and their trajectories be followed. Simulations of the 1D-Gross-Pitaevskii equation have been performed to compare the experiment with a mean-field description.”

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Publication: Physical Review Letters
Issue/Year: Phys. Rev. Lett. 101, Issue 12, 120406 (2008)
DOI: 10.1103/PhysRevLett.101.120406

Hydrodynamic interactions in two dimensions

Author(s): R. Di Leonardo, S. Keen, F. Ianni, J. Leach, M. J. Padgett and G. Ruocco

Abstract:

“We measure hydrodynamic interactions between colloidal particles confined in a thin sheet of fluid. The reduced dimensionality, compared to a bulk fluid, increases dramatically the range of couplings. Using optical tweezers we force a two body system along the eigenmodes of the mobility tensor and find that eigenmobilities change logarithmically with particle separation. At a hundred radii distance, the mobilities for rigid and relative motions differ by a factor of 2, whereas in bulk fluids, they would be practically indistinguishable. A two dimensional counterpart of Oseen hydrodynamic tensor quantitatively reproduces the observed behavior, once the relevant boundary conditions are recognized. These results highlight the importance of dimensionality for transport and interactions in colloidal systems and proteins in biological membranes.”

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Publication: Physical Review E
Issue/Year: Phys. Rev. E 78, Issue 3, 031406 (2008)
DOI: 10.1103/PhysRevE.78.031406

Universal Optimal Transmission of Light Through Disordered Materials

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

Abstract:

“We experimentally demonstrate increased diffuse transmission of light through strongly scattering materials. Wave front shaping is used to selectively couple light to the open transport eigenchannels, specific solutions of Maxwell’s equations which the sample transmits fully, resulting in an increase of up to 44% in the total angle-integrated transmission compared to the case where plane waves are incident. The results for each of several hundreds of experimental runs are in excellent quantitative agreement with random matrix theory. From our measurements we conclude that with perfectly shaped wave fronts the transmission of a disordered sample tends to a universal value of 2/3, regardless of the thickness.”

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Publication: Physical Review Letters
Issue/Year: Phys. Rev. Lett., Volume 101, Issue 12, 120601 (2008)
DOI: 10.1103/PhysRevLett.101.120601

Novel approaches to the design of halftone masks for analog lithography

Author(s): Marcel Teschke and Stefan Sinzinger

Abstract:

“We report novel approaches to the design of halftone masks for analog lithography. The approaches are derived from interferometric phase contrast. In a first step we show that the interferometric phase-contrast method with detour holograms can be reduced into a single binary mask. In a second step we introduce the interferometric phase-contrast method by interference of the object wavefront with the conjugate object wavefront. This method also allows for a design of a halftone mask. To use kinoform holograms as halftone phase masks, we show in a third step the combination of the zeroth-order phase-contrast technique with the interferometric phase-contrast method.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 47, Issue 26, pp. 4767-4776 (2008)
DOI: 10.1364/AO.47.004767

Hologram optimization for SLM-based reconstruction with regard to polarization effects

Author(s): C. Kohler, T. Haist, X. Schwab, and W. Osten

Abstract:

“We report on first results obtained with two modified hologram optimization algorithms. These algorithms take into account the complex modulation characteristic of the spatial light modulators employed for hologram reconstruction. To this end the Jones matrices of the modulator as well as all other components of the setup are used within a modified direct binary search and an iterative Fourier transform algorithm. Geometrical phase effects are included in the optimization. Elimination of the analyzer behind the spatial light modulator is possible by that approach and for typical setups using twisted-nematic liquid crystal modulators an enhanced overall diffraction efficiency is achieved. Possible applications are the comparative digital holography and optical tweezers. Experimental results for the reconstructions of holograms with a Holoeye LC-R 3000 modulator are presented.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 19, pp. 14853-14861 (2008)
DOI: 10.1364/OE.16.014853

A new method for three-dimensional tracking using a liquid crystal on silicon (LCoS)

Author(s): Matías A Goldin, Guadalupe Díaz Costanzo, Oscar E Martínez, Claudio Iemmi, Silvia Ledesma

Abstract:

“Imaging of samples by different microscopy techniques has produced a relevant impact in the development of new diagnosis techniques in biology, medicine, and material science. In many biological applications, where the sample changes or moves during the observation, a dynamical focusing of the microscope is needed. To this end it is necessary to localize the sample previously to the refocusing process. We introduce here an optical system that can perform three-dimensional (3D) tracking without mechanical displacements. The system is based on the use of a high resolution liquid crystal on silicon (LCoS) device working as a phase mostly wavefront modulator. The additional advantage of this system is performing the motion of the spot at video rate. By using elliptical polarization we have experimentally found a configuration where the phase modulation is 2π and the intensity modulation has a variation less than 25%. For this configuration we show how the spot can be moved through the focus plane by means of linear phases, or displaced out of this plane by using a quadratic phase.”

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Publication: Journal of Optics A
Issue/Year: J. Opt. A: Pure Appl. Opt., Volume 10, Number 10, pp. 104001
DOI: 10.1088/1464-4258/10/10/104001

Spatial fluorescence cross-correlation spectroscopy by means of a spatial light modulator

Author(s): Yoann Blancquaert, Jie Gao, Jacques Derouard, Antoine Delon

Abstract:

“Spatial fluorescence cross-correlation spectroscopy is a rarely investigated version of fluorescence correlation spectroscopy, in which the fluorescence signals from different observation volumes are cross-correlated. In the reported experiments, two observation volumes, typically shifted by a few µm, are produced, with a spatial light modulator and two adjustable pinholes. We illustrated the feasibility and potentiality of this technique by: i) measuring molecular flows, in the range 0.2-1.5 µm/ms, of solutions seeded with fluorescent nanobeads or rhodamine molecules (simulating active transport phenomenons); ii) investigating the permeability of the phospholipidic membrane of giant unilamellar vesicles versus hydrophilic or hydrophobic molecules (in that case the laser spots were set on both sides of the membrane). Theoretical descriptions are proposed together with a discussion about fluorescence-correlation-spectroscopy-based, alternative methods.”

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Publication: Journal of Biophotonics
Issue/Year: Journal of Biophotonics, Volume 1 Issue 5, Pages 408 – 418 (2008)
DOI: 10.1002/jbio.200810007

Applications of LCoS-based adaptive optical elements in microscopy

Author(s): Andreas Hermerschmidt, Jan Haffner, Tobias Haist, Wolfgang Osten

Abstract:

“Liquid crystal on silicon (LCoS)-based spatial light modulators (SLMs) are versatile adaptive optical elements. In microscopy, among their applications are aberration sensing and correction in wide-field microscopy and also the implementation of holographic optical tweezers. For aberration correction, the required scene-based wavefront sensing can be implemented as a modified correlation-based Shack-Hartmann approach where a high-resolution SLM first senses and then corrects the aberrations. For the implementation of holographic optical tweezers, the SLM serves as a variable optical beam-splitter which is addressed with holograms computed by fast algorithms implemented on the graphics processing unit (GPU) of a common PC almost in real-time.”

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Publication: Proceedings IEEE/LEOS Internationall Conference on Optical MEMs and Nanophotonics
Issue/Year: Proceedings IEEE/LEOS Internationall Conference on Optical MEMs and Nanophotonics, 2008,
DOI: 10.1109/OMEMS.2008.4607842

Implementation of phase-only modulation utilizing a twisted nematic liquid crystal spatial light modulator

Author(s): Mohammad Sultan Mahmud, Izabela Naydenova and Vincent Toal

Abstract:

“Twisted nematic liquid crystal spatial light modulators (SLM) are widely used for amplitude modulation of light. The technique for measuring phase and amplitude modulation introduced by a twisted nematic cell is not new but the novelty here is that, after characterization of a Holoeye LC2002 TNLC device, we were able to identify specific conditions that allow for its use as a pure 180° or more phase modulator with little or no amplitude modulation at 514.5 nm laser wavelength. The phase shift introduced by the SLM was measured using a near common-path Mach–Zehnder interferometer. The experimentally measured and the theoretically predicted intensity transmission and phase shift as functions of gray levels are compared. Finally, the effects of errors in the angular settings of the polarizers and quarter waveplates on the intensity transmission and phase shift are studied.”

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Publication: Journal of Optics A
Issue/Year: J. Opt. A: Pure Appl. Opt. 10 085007 (7pp), 2008
DOI: 10.1088/1464-4258/10/8/085007

Femtosecond pulse shaping in two dimensions: Towards higher complexity optical waveforms

Author(s): V. R. Supradeepa, Chen-Bin Huang, Daniel E. Leaird, Andrew M. Weiner

Abstract:

“We demonstrate a new Fourier pulse shaping apparatus capable of achieving simultaneous high resolution and broad bandwidth operation by dispersing frequency components in a two dimensional geometry through simultaneous use of a high resolution and a broad bandwidth spectral disperser. We show experimental results which demonstrate significant improvements in achievable waveform complexity (number of controllable temporal/spectral features). We also demonstrate experiments of line-by-line pulse shaping with optical frequency combs. In this regime our configuration would allow significant enhancement of the number of controllable spectral lines which may further enhance recently demonstrated massively parallel approaches to spectroscopic sensing using frequency combs.”

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Publication:Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 16, pp. 11878-11887 (2008)
DOI: 10.1364/OE.16.011878
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