Mixing via thermocapillary generation of flow patterns inside a microfluidic drop

Author(s): María Luisa Cordero, Hans Olav Rolfsnes, Daniel R Burnham, Paul A Campbell, David McGloin, Charles N Baroud

Abstract:

“The heating produced by a focused laser has been shown to provide a range of manipulation tools on droplets in microfluidic situations, through the generation of thermocapillary flows whose net result is to produce a force on the drop. In particular, droplets of water in oil that are produced in microchannels can be blocked in a special test section. Here, the manipulation of the flow within the droplet is explored through spatial and temporal modulation of the laser pattern used to block the drop. When a stationary pattern of two laser spots is used, the flow preserves the mirror symmetry inside the drop, as happens in the case of two alternating spots if the frequency of the switching is higher than the response rate of the fluid. Lower frequency switching produces a time periodic flow that breaks the mirror symmetry and which leads to efficient mixing inside the droplet. The mixing that is produced by this alternating flow is studied both experimentally and using numerical simulations of particle trajectories from measured velocity fields. This mixing can be optimized for certain parameter ranges, namely by varying the distance between the spots and the forcing frequency.”

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Publication: New Journal of Physics
Issue/Year: New Journal of Physics, Volume 11, July 2009
DOI: 10.1088/1367-2630/11/7/075033

Spiral phase filtering and orientation-selective edge detection/enhancement

Author(s): Guohai Situ, Giancarlo Pedrini, Wolfgang Osten

Abstract:

“A spiral phase plate with an azimuthal structure exp[iϕ](0⩽ϕ<2π) has been used as a filter in a 4f system to achieve edge enhancement. Generally such edge-enhanced effect is isotropic, i.e., each edge of an input pattern is enhanced to the same degree regardless of its orientation. We found that one can achieve anisotropic edge enhancement by breaking down the symmetry of the filtering process. This can be done in two ways: first, by use of a fractional spiral phase filter (SPF) with a fractional topological charge and a controllable orientation of the edge discontinuity, and second, by the lateral shifting of the SPF. We interpret this process as a vortex formation due to the diffraction of the Fourier spectrum of the input pattern by a SPF with an integer and fractional topological charge. Optical experiments using a spatial light modulator were carried out to verify our proposal.”

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Publication: J. Opt. Soc. Am. A
Issue/Year: JOSA A, Vol. 26, Issue 8, pp. 1788-1797 (2009)
DOI: 10.1364/JOSAA.26.001788

3-D coherence holography using a modified Sagnac radial shearing interferometer with geometric phase shift

Author(s): Dinesh N. Naik, Takahiro Ezawa, Yoko Miyamoto, and Mitsuo Takeda

Abstract:

“A new image reconstruction scheme for coherence holography using a modified Sagnac-type radial shearing interferometer with geometric phase shift is proposed, and the first experimental demonstration of generic Leith-type coherence holography, which reconstructs off-axis 3-D objects with depth information, is presented. The reconstructed image, represented by a coherence function, can be visualized with a controllable magnification, which opens up a new possibility for a coherence imaging microscope.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 17, Issue 13, pp. 10633-10641
DOI: 10.1364/OE.17.010633

Microdisplays in holographic mastering applications

Author(s): Sven Plöger, Sven Krüger, Stefan Osten, Günther Wernicke

Abstract:

“We demonstrate implementation and performance of microdisplay systems based on liquid-crystal technology in a variety of applications in holographic mastering. These displays can encode 2D objects information in grey scale or address holographic patterns in amplitude or phase. The main advantage is here to address any content dynamically with typically 60 Hz. Furthermore they show a resolution up to 1920×1200 pixels with a pixel size as small as 6.4 microns. Therefore they are extremely suitable for a dynamic or multi-exposure mastering process, to incorporate image content, phase-encode objects or any holographic features. This technology is already being used in holographic security applications as well as in commercial and display holography. We report about a few applications/implementations and show experimental results and performance parameters.”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE, Vol. 7358, 73581H (2009);
DOI: 10.1117/12.823474

Poincaré-sphere representation of phase-mostly twisted nematic liquid crystal spatial light modulators

Author(s): V Durán, P Clemente, Ll Martínez-León, V Climent, J Lancis

Abstract:

“We establish necessary conditions in order to build a phase-only wavefront modulation system from a liquid crystal display. These conditions determine the dependence of the polarization state of the light emerging from the display on the addressing gray level. The analysis, which is carried out by means of the coherence-matrix formalism, includes the depolarization properties of the device. Two different types of polarization distributions at the output of the liquid crystal cells are found. This approach is applied to a twisted nematic liquid crystal display. In this case, an optimization algorithm must be designed in order to select the input polarization state that leads to the required distributions. We show that the Poincaré-sphere representation provides a convenient framework to design the optimization algorithm as it allows for a reduced number of degrees of freedom. This feature significantly decreases the computation time. Laboratory results are presented for a liquid crystal on silicon display showing a phase modulation depth greater than 2π rad with an intensity variation lower than 6%. In addition, a hybrid ternary modulation (HTM), an operation regime employed in holographic data storage, is achieved.”

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Publication: Journal of Optics A
Issue/Year: J. Opt. A: Pure Appl. Opt. (2009), Opt. 11 085403
DOI: 10.1088/1464-4258/11/8/085403

Influence of the incident angle in the performance of Liquid Crystal on Silicon displays

Author(s): A. Lizana, N. Martín, M. Estapé, E. Fernández, I. Moreno, A. Márquez, C. Iemmi, J. Campos, and M. J. Yzuel

Abstract:

“In this paper we experimentally analyze the performance of a twisted nematic liquid crystal on silicon (LCoS) display as a function of the angle of incidence of the incoming beam. These are reflective displays that can be configured to produce amplitude or phase modulation by properly aligning external polarization elements. But we demonstrate that the incident angle plays an important role in the selection of the polarization configuration. We performed a Mueller matrix polarimetric analysis of the display that demonstrates that the recently reported depolarization effect observed in this type of displays is also dependant on the incident angle. ”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 17, Issue 10, pp. 8491-8505 (2009)
DOI: 10.1364/OE.17.008491

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

Model-free method for measuring the full Jones matrix of reflective liquid-crystal displays

Author(s): Christian Kohler, Tobias Haist, Wolfgang Osten

Abstract:

“We present a method for measuring all eight parameters (including the signs) of the Jones matrices of liquid-crystal displays. The method can be applied to measure the Jones matrices for all addressable gray levels thus delivering the specifications needed for calculating characteristic curves for arbitrary input and output polarizations. Unlike other approaches, we do not rely on a physical model of the LCD. Thus, it is possible to measure the Jones matrices of a more complex optical system in one step (e.g., when a reflective LCD is used in combination with a beamsplitter). Though the method presented is, in principle, applicable for transmissive and reflective LCDs, calculations and experiments are only shown using the example of a reflective liquid-crystal-on-silicon display. ”

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Publication: SPIE – Optical Engineering
Issue/Year: SPIE – Optical Engineering, Vol. 48, 044002 (2009)
DOI: 10.1117/1.3119309

Programmable two-dimensional optical fractional Fourier processor

Author(s): Jose Augusto Rodrigo, Tatiana Alieva, Maria L. Calvo

Abstract:

“A flexible optical system able to perform the fractional Fourier transform (FRFT) almost in real time is presented. In contrast to other FRFT setups the resulting transformation has no additional scaling and phase factors depending on the fractional orders. The feasibility of the proposed setup is demonstrated experimentally for a wide range of fractional orders. The fast modification of the fractional orders, offered by this optical system, allows to implement various proposed algorithms for beam characterization, phase retrieval, information processing, etc.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 17, Issue 7, pp. 4976-4983 (2009)
DOI: 10.1364/OE.17.004976

A novel three-dimensional holographic display system based on LC-R2500 spatial light modulatora

Author(s): Huadong Zheng, Yingjie Yu, Cuixia Dai

Abstract:

“A novel holographic display system is proposed in this paper. The system takes LC-R2500, a kind of reflective liquid crystal spatial light modulator, (LC-SLM) as the core display unit, which can meet the requirement of real-time reconstruction of three-dimensional (3D) objects from holograms in free space. The relationship between hologram recording and image reconstruction is discussed, and the parameters associated with the magnification of reconstructed image over original object are determined. Experimental results of holographic display using the system are also given in the end.”

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Publication: Optik – International Journal for Light and Electron Optics
Issue/Year: Optik – International Journal for Light and Electron Optics, Volume 120, Issue 9, May 2009, Pages 431-436
DOI: 10.1016/j.ijleo.2007.11.002
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