Phase contrast enhancement in microscopy using spiral phase filtering

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

Abstract:

“We demonstrate two methods based on Fourier plane filtering using (a) a fractional spiral phase plate (SPP) and (b) an off-axial SPP for phase contrast enhancement in optical microscopy. In comparison to previous works, a spatially incoherent LED is used in the Köhler illumination as the light source to illuminate the biological specimen. We demonstrate that both these methods can transform the phase specimen into a relief-like view even under such illumination. The degree and orientation of enhancement can be controlled by changing the phase structure of the filter. The SPP is displayed on a phase-only spatial light modulator, and can be integrated into the optical path of standard microscopes.”

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Publication: Optics Communications, (subscription required)

Issue/Year/DOI: Optics Communications, Volume 283, Issue 7, 1 April 2010, Pages 1273–1277
doi:10.1016/j.optcom.2009.11.084

Self-reference quantitative phase microscopy for microfluidic devices

Author(s): Jaeduck Jang, Chae Yun Bae, Je-Kyun Park, Jong Chul Ye

Abstract:

“This Letter describes a quantitative phase microscopy for microfluidic devices using a simple self-referencing interferometry. Compared with the gross dimensions of the microfluidic device, the microchannel occupies only a small area of the device. Hence, the reference field can be generated by inverting the relative position of the specimen and background. Our system is realized using an extended depth-of-field optics in the form of Michelson interferometry, which allows quantitative phase measurement for an increased depth-of-field without moving objective lens or specimen. Furthermore, the system can be readily converted to a higher signal-to-noise ratio Hilbert phase microscopy thanks to the simultaneous acquisition of double interferograms. The performance of our system is verified using polymer beads, micropatterning poly(dimethylsiloxane) (PDMS), and embryo cells in the microchannels.”

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Publication: Optics Letters (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 35, Issue 4, pp. 514-516 (2010)
doi:10.1364/OL.35.000514

Self-reference extended depth-of-field quantitative phase microscopy

Author(s): Jaeduck Jang, Chae Yun Bae, Je-Kyun Park, and Jong Chul Ye

Abstract:

“This paper describes a novel quantitative phase microscopy based on a simple self-referencing scheme using Michelson interferometry. In order to achieve the homogeneous reference field for accurate phase measurement, the imaging field-of-view (FOV) is split onto the sample and homogenous background areas. The reference field can be generated by rotating the relative position of the sample and homogenous background in the object arm. Furthermore, our system is realized using an extended depth-of-field (eDOF) optics, which allows quantitative phase measurement for an increase of the depth-of-field without moving objective lens or specimen. The proposed method is confirmed by experimental results using various samples such as polystyrene beads and red blood cells (RBCs).”

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Publication: SPIE Proceedings / Volume 7570, (subscription required)

Issue/Year/DOI: Proc. SPIE 7570, 757018 (2010)
doi:10.1117/12.843082

Plasmid copy number noise in monoclonal populations of bacteria

Author(s): Jérôme Wong Ng, Didier Chatenay, Jérôme Robert, Michael Guy Poirier

Abstract:

“Plasmids are extra chromosomal DNA that can confer to their hosts’ supplementary characteristics such as antibiotic resistance. Plasmids code for their copy number through their own replication frequency. Even though the biochemical networks underlying the plasmid copy number (PCN) regulation processes have been studied and modeled, no measurement of the heterogeneity in PCN within a whole population has been done. We have developed a fluorescent-based measurement system, which enables determination of the mean and noise in PCN within a monoclonal population of bacteria. Two different fluorescent protein reporters were inserted: one on the chromosome and the other on the plasmid. The fluorescence of these bacteria was measured with a microfluidic flow cytometry device. We show that our measurements are consistent with known plasmid characteristics. We find that the partitioning system lowers the PCN mean and standard deviation. Finally, bacterial populations were allowed to grow without selective pressure. In this case, we were able to determine the plasmid loss rate and growth inhibition effect.”

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Publication: Physical Review E, (subscription required)

Issue/Year/DOI: Phys. Rev. E, Volume 81, Issue 1, 011909 (2010)
DOI:10.1103/PhysRevE.81.011909

Nonspherical laser-induced cavitation bubbles

Author(s): Kang Yuan Lim, Pedro A. Quinto-Su, Evert Klaseboer, Boo Cheong Khoo, Vasan Venugopalan, Claus-Dieter Ohl

Abstract:

“The generation of arbitrarily shaped nonspherical laser-induced cavitation bubbles is demonstrated with a optical technique. The nonspherical bubbles are formed using laser intensity patterns shaped by a spatial light modulator using linear absorption inside a liquid gap with a thickness of 40 μm. In particular we demonstrate the dynamics of elliptic, toroidal, square, and V-shaped bubbles. The bubble dynamics is recorded with a high-speed camera at framing rates of up to 300 000 frames per second. The observed bubble evolution is compared to predictions from an axisymmetric boundary element simulation which provides good qualitative agreement. Interesting dynamic features that are observed in both the experiment and simulation include the inversion of the major and minor axis for elliptical bubbles, the rotation of the shape for square bubbles, and the formation of a unidirectional jet for V-shaped bubbles. Further we demonstrate that specific bubble shapes can either be formed directly through the intensity distribution of a single laser focus, or indirectly using secondary bubbles that either confine the central bubble or coalesce with the main bubble. The former approach provides the ability to generate in principle any complex bubble geometry.”

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Publication: Physical Review E, (subscription required)

Issue/Year/DOI: Phys. Rev. E, Volume 81, Issue 1, 016308 (2010)
DOI:10.1103/PhysRevE.81.016308

Adaptive optics via pupil segmentation for high-resolution imaging in biological tissues

Author(s): Na Ji, Daniel E Milkie, Eric Betzig

Abstract:

“Biological specimens are rife with optical inhomogeneities that seriously degrade imaging performance under all but the most ideal conditions. Measuring and then correcting for these inhomogeneities is the province of adaptive optics. Here we introduce an approach to adaptive optics in microscopy wherein the rear pupil of an objective lens is segmented into subregions, and light is directed individually to each subregion to measure, by image shift, the deflection faced by each group of rays as they emerge from the objective and travel through the specimen toward the focus. Applying our method to two-photon microscopy, we could recover near-diffraction–limited performance from a variety of biological and nonbiological samples exhibiting aberrations large or small and smoothly varying or abruptly changing. In particular, results from fixed mouse cortical slices illustrate our ability to improve signal and resolution to depths of 400 μm.”

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Publication: Nature Methods, (subscription required)

Issue/Year/DOI: Nature Methods 7, 141 – 147 (2009)
doi:10.1038/nmeth.1411

Rotating single atoms in a ring lattice generated by a spatial light modulator

Author(s): Xiaodong He, Peng Xu, Jin Wang, and Mingsheng Zhan

Abstract:

“We demonstrated trapping single neutral Rb atoms in micro traps of an optical ring lattice formed by superposing the ±l components of the Laguerre-Gaussian mode, and generated by reflecting a single laser beam from a computer controlled spatial light modulator. A single atom in one trap or two atoms with one each in two traps were identified by observing the fluorescence. The trap array loaded with single atoms was rotated by dynamically displaying the hologram animation movie on the modulator. The modulation period in the fluorescence indicates the rotation of one or two single atoms in the lattice.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 17, Issue 23, pp. 21007-21014 (2009)
doi:10.1364/OE.17.021007

Optical mirror trap with a large field of view

Author(s): Maximilian Pitzek, Ruth Steiger, Gregor Thalhammer, Stefan Bernet, and Monika Ritsch-Marte

Abstract:

“Holographic optical tweezers typically require microscope objectives with high numerical aperture and thus usually suffer from the disadvantage of a small field of view and a small working distance. We experimentally investigate an optical mirror trap that is created after reflection of two holographically shaped collinear beams on a mirror. This approach combines a large field of view and a large working distance with the possibility to manipulate particles in a large size range, since it allows to use a microscope objective with a numerical aperture as low as 0.2. In this work we demonstrate robust optical three-dimensional trapping in a range of 1mm x 1mm x 2mm with particle sizes ranging from 1.4 μm up to 45 μm. The use of spatial light modulator based holographic methods to create the trapping beams allows to simultaneously trap many beads in complex, dynamic configurations. We present measurements that characterize the mirror traps in terms of trap stiffness, maximum trapping force and capture range.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 17, Issue 22, pp. 19414-19423 (2009)
doi:10.1364/OE.17.019414

Compact Optical Tweezers Based on SLM for Real-Time Optical Trapping and Manipulation

Author(s): Martin Nyvlt, Marek Skeren

Abstract:

“We report a compact holographic optical tweezers based on an LCoS SLM. Optical traps are generated by diffraction of light on the Fresnel-type hologram generated by a fast parallel algorithm that enables real-time 3-D manipulation.”

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Publication: Conference Paper Frontiers in Optics (FiO) – via Optics InfoBase, (subscription required)

Issue/Year/DOI: onference Paper Frontiers in Optics (FiO), October 11, 2009

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.”

Link to Publications Page

Publication: New Journal of Physics, (free download)

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

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