A spatial light phase modulator with an effective resolution of 4 mega-pixels

Author(s): Daryl Preece; Eric Yao; Graham Gibson; Richard Bowman; Jonathan Leach; Miles Padgett


“We report the design, construction and characterization of a 4 mega-pixel, optically-addressed, spatial light modulator (OSLM). The intensity distribution corresponding to a kinoform is displayed across two wide-screen liquid crystal on silicon displays, the images of which are combined and relayed to the address face of a 40 mm aperture OSLM. This spatially varying intensity profile is converted into a phase hologram on the readout side of the OSLM. When illuminated at 532 nm we measure a first-order diffraction efficiency of ≈50% at 400 line pairs and ≈20% at 900 line pairs. We show that aberration associated with the non-flatness of the device can be corrected within software by modification of the hologram.”

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Publication: Journal of Modern Optics, (subscription required)

Issue/Year/DOI: Journal of Modern Optics, Volume 55, Issue 18 October 2008 , pages 2945 – 2951
DOI: 10.1080/09500340802272357

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


“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, (subscription required)

Issue/Year/DOI: Phys. Rev. Lett. 101, Issue 12, 120406 (2008)

Oscillations and interactions of dark and dark–bright solitons in Bose–Einstein condensates

Author(s): Christoph Becker, Simon Stellmer, Parvis Soltan-Panahi, Sören Dörscher, Mathis Baumert, Eva-Maria Richter, Jochen Kronjäger, Kai Bongs & Klaus Sengstock


“Solitons are among the most distinguishing fundamental excitations in a wide range of nonlinear systems such as water in narrow channels, high-speed optical communication, molecular biology and astrophysics. Stabilized by a balance between spreading and focusing, solitons are wave packets that share some exceptional generic features such as form stability and particle-like properties. Ultracold quantum gases represent very pure and well-controlled nonlinear systems, therefore offering unique possibilities to study soliton dynamics. Here, we report on the observation of long-lived dark and dark–bright solitons with lifetimes of up to several seconds as well as their dynamics in highly stable optically trapped 87Rb Bose–Einstein condensates. In particular, our detailed studies of dark and dark–bright soliton oscillations reveal the particle-like nature of these collective excitations for the first time. In addition, we discuss the collision between these two types of solitary excitation in Bose–Einstein condensates.”

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Publication: Nature Physics, (free download)

Issue/Year/DOI: Nature Physics 4, 496 – 501 (2008)

Optically driven pumps and flow sensors for microfluidic systems

Author(s): H Mushfique, J Leach, R Di Leonardo, M J Padgett, J M Cooper


“This paper describes techniques for generating and measuring fluid flow in microfluidic devices. The first technique is for the multi-point measurement of fluid flow in microscopic geometries. The flow sensing method uses an array of optically trapped microprobe sensors to map out the fluid flow. The optical traps are alternately turned on and off such that the probe particles are displaced by the flow of the surrounding fluid and then retrapped. The particles’ displacements are monitored by digital video microscopy and directly converted into velocity field values. The second is a method for generating flow within a microfluidic channel using an optically driven pump. The optically driven pump consists of two counter-rotating birefringent vaterite particles trapped within a microfluidic channel and driven using optical tweezers. The transfer of spin angular momentum from a circularly polarized laser beam causes the particles to rotate at up to 10 Hz. The pump is shown to be able to displace fluid in microchannels, with flow rates of up to 200 m-3 s-1 (200 fL s-1). In addition a flow sensing method, based upon the technique mentioned above, is incorporated into the system in order to map the magnitude and direction of fluid flow within the channel.”

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Publication: Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, (subscription required)

Issue/Year/DOI: Journal of Mechanical Engineering Science, Volume 222, Number 5 / 2008, Pages 829-837

Improved micro topography measurement by LCoS-based fringe projection and z-stitching

Author(s): X. Schwab, C. Kohler, K. Körner, N. Eichhorn, W. Osten


“Fringe projection is a commonly used method for 3D surface metrology. Numerous applications have demonstrated a measurement field from a few millimeters to several meters. To enable the measurement of micro systems with this method, a zoom stereo microscope from Leica was used as the basis for the implementation of a fringe projection microscope. A state of the art twisted nematic WUXGA LCD was used for flexible fringe generation. The high fill factor of this reflective LCoS in combination with a 500 Lumen LED and a 12 bit CCD camera delivers fringe patterns with high contrast. This allows us to measure objects with both a strong reflectivity variation and a low reflectivity. The second main objective was to increase the measurement field and the depth of field. Using the zoom system and exchangeable microscope objectives, the measurement fields could be changed quickly from 4 cm² to less than 1 mm². Depending on the measurement field, the depth of field was between 5.22 mm and 0.018 mm. However, this was often not sufficient to measure the complete depth of a 3D-object. The microscope system also features an integrated high precision motor stage, which is already used for system calibration. Based on this, we implemented a new z-stitching method where n measurements at different well determined z-positions of the motor stage were performed. The n resulting topography maps can be stitched together to get the complete depth map of the entire object. Thus the depth measurement range is only limited by the mechanics of the z-stage. ”

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Publication: SPIE Proceedings, (subscription required)

Issue/Year/DOI: Proc. SPIE, Vol. 6995, 69950Q (2008);