Optical macro-tweezers: trapping of highly motile micro-organisms

Author(s): G Thalhammer, R Steiger, S Bernet and M Ritsch-Marte

Abstract:

“Optical micromanipulation stands for contact-free handling of microscopic particles by light. Optical forces can manipulate non-absorbing objects in a large range of sizes, e.g., from biological cells down to cold atoms. Recently much progress has been made going from the micro- down to the nanoscale. Less attention has been paid to going the other way, trapping increasingly large particles. Optical tweezers typically employ a single laser beam tightly focused by a microscope objective of high numerical aperture to stably trap a particle in three dimensions (3D). As the particle size increases, stable 3D trapping in a single-beam trap requires scaling up the optical power, which eventually induces adverse biological effects. Moreover, the restricted field of view of standard optical tweezers, dictated by the use of high NA objectives, is particularly unfavorable for catching actively moving specimens. Both problems can be overcome by traps with counter-propagating beams. Our ‘macro-tweezers’ are especially designed to trap highly motile organisms, as they enable three-dimensional all-optical trapping and guiding in a volume of 2 × 1 × 2 mm³. Here we report for the first time the optical trapping of large actively swimming organisms, such as for instance Euglena protists and dinoflagellates of up to 70 µm length. Adverse bio-effects are kept low since trapping occurs outside high intensity regions, e.g., focal spots. We expect our approach to open various possibilities in the contact-free handling of 50–100 µm sized objects that could hitherto not be envisaged, for instance all-optical holding of individual micro-organisms for taxonomic identification, selective collecting or tagging.”

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Publication: Journal of Optics, (subscription required)

Issue/Year/DOI: J. Opt. 13 (2011) 044024 (6pp),
doi:10.1088/2040-8978/13/4/044024

Optimal resolution in Fresnel incoherent correlation holographic fluorescence microscopy

Author(s): Gary Brooker, Nisan Siegel, Victor Wang, and Joseph Rosen

Abstract:

“Fresnel Incoherent Correlation Holography (FINCH) enables holograms and 3D images to be created from incoherent light with just a camera and spatial light modulator (SLM). We previously described its application to microscopic incoherent fluorescence wherein one complex hologram contains all the 3D information in the microscope field, obviating the need for scanning or serial sectioning. We now report experiments which have led to the optimal optical, electro-optic, and computational conditions necessary to produce holograms which yield high quality 3D images from fluorescent microscopic specimens. An important improvement from our previous FINCH configurations capitalizes on the polarization sensitivity of the SLM so that the same SLM pixels which create the spherical wave simulating the microscope tube lens, also pass the plane waves from the infinity corrected microscope objective, so that interference between the two wave types at the camera creates a hologram. This advance dramatically improves the resolution of the FINCH system. Results from imaging a fluorescent USAF pattern and a pollen grain slide reveal resolution which approaches the Rayleigh limit by this simple method for 3D fluorescent microscopic imaging.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 19, Issue 6, pp. 5047-5062 (2011)
doi:10.1364/OE.19.005047

Dynamic generation of Debye diffraction-limited multifocal arrays for direct laser printing nanofabrication

Author(s): Han Lin, Baohua Jia, and Min Gu

Abstract:

“We propose a Debye-theory-based iterative method to produce accurate phase patterns for generating highly uniform diffraction-limited multifocal arrays with a high-NA objective. It is shown that by using the Debye method, the uniformity of the diffraction-limited focal arrays can reach 99%, owing to the critical consideration of the depolarization effect associated with high-NA objectives. The generated phase patterns are implemented in fast dynamic laser printing nanofabrication for the generation of individually controlled high-quality microvoid arrays in a solid polymer material by a single exposure of a femtosecond laser beam. As a result of the high-quality multifocal arrays, functional three-dimensional photonic crystals possessing multiple stopgaps with suppression up to 80% in transmission spectra are demonstrated.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 36, Issue 3, pp. 406-408 (2011)
doi:10.1364/OL.36.000406

Flexible contrast for low-coherence interference microscopy by Fourier-plane filtering with a spatial light modulator

Author(s): Stefan E. Schausberger, Bettina Heise, Christian Maurer, Stefan Bernet, Monika Ritsch-Marte, and David Stifter

Abstract:

“We propose a full-field low-coherence interference (LCI) microscope that can provide different contrast modes using Fourier-plane filtering by means of a spatial light modulator. By altering the phase and spatial frequencies of the backreflected wavefront from the sample arm of the interferometer, we are able to change the contrast in the depth-resolved LCI images. We demonstrate that different types of contrast modes, such as, e.g., spiral phase contrast, can successfully be emulated to provide specific enhancement of internal structures and edges and to reveal complementary details within the samples under investigation.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 35, Issue 24, pp. 4154-4156 (2010)
doi:10.1364/OL.35.004154

Isotropic Diffraction-Limited Focusing Using a Single Objective Lens

Author(s): Emeric Mudry, Eric Le Moal, Patrick Ferrand, Patrick C. Chaumet, and Anne Sentenac

Abstract:

“Focusing a light beam through a lens produces an anisotropic spot elongated along the optical axis, because the light comes from only one side of the focal point. Using the time-reversal concept, we show that isotropic focusing can be realized by placing a mirror after the focal point and shaping the incident beam. This idea is applied to confocal microscopy and brings about a dramatic improvement of the axial resolution.”

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Publication: Physical Review Letters, (subscription required)

Issue/Year/DOI: Phys. Rev. Lett., Volume 105, 203903 (2010)
doi:10.1103/PhysRevLett.105.203903

Combination of scene-based and stochastic measurement for wide-field aberration correction in microscopic imaging

Author(s):

Michael Warber, Selim Maier, Tobias Haist, and Wolfgang Osten

Abstract:

“We report on a novel aberration correction technique that uses the sequential combination of two different aberration measurement methods to correct for setup-induced and specimen-induced aberrations. The advantages of both methods are combined and, thus, the measurement time is strongly reduced without loss of accuracy. The technique is implemented using a spatial-light-modulator-based wide-field microscope without the need for additional components (e.g., a Shack–Hartmann sensor). The aberrations are measured without a reference object by directly using the specimen to be imaged. We demonstrate experimental results for technical as well as biological specimens.”

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Publication: Applied Optics

Issue/Year/DOI: Vol. 49, Issue 28, pp. 5474-5479 (2010)
DOI: 10.1364/AO.49.005474

Optically based manufacturing with polymer particles

Author(s): Reza Ghadiri, Mario Surbek, Cemal Esen, Andreas Ostendorf.

Abstract:

“We present a new single-laser optical trapping technique for the exact manipulation and durable assembly of transparent polymer microparticles. This technique comprises the trapping of microparticles and the assembly by using a laser-driven thermal process for the joining of the particles. The thermal energy necessary for the systematic joining is applied partly by global heating of the processing chamber and by absorption of the electromagnetic radiation of the laser tweezer. The main advantage of this contact free joining technology is to use the same laser for the optical trapping, positioning and the durable assembly. The generated joints are stable and cannot be broken up with optical forces. In summary, a new micromanufacturing process based on an optical machining process is reported with promising applications in the MEMS and photonics area.”

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Publication: Physics Procedia, (free download)

Issue/Year/DOI: Physics Procedia, Volume 5, Part A, Pages 47–51, (2010)
doi:10.1016/j.phpro.2010.08.121

Optical control and dynamic patterning of zeolites

Author(s): Mike Woerdemann, Christina Alpmann, Florian Hörner, Cornelia Denz, André Devaux and Luisa De Cola

Abstract:

“Zeolite crystals have a wide use as model systems for artificial light harvesting systems, as nano-containers for supramolecular organization or as building blocks for 1D and 2D assemblies of several crystals. In particular the assembly of zeolite L crystals with the aim to bridge the gap between the nano- and the macroscopic world has been a focus of research during the last years. However, almost all available approaches to order, assemble and pattern Zeolite L are restricted to large amounts of crystals. Although these approaches have proven to be powerful for many applications, but they have only limited control over positioning or orientation of single crystals and are lacking if patterns or structures are required which are composed of a few or up to a few hundred individual crystals. We demonstrate here that holographic optical tweezers are a powerful and versatile instrument to control zeolite L on the single crystal level. It is shown that full three-dimensional positioning, including rotational control, of any zeolite L crystal can be achieved. Finally, we demonstrate fully reversible, dynamic patterning of a multitude of individually controlled zeolite L crystals.”

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Publication: SPIE Proceedings, (subscription required)

Issue/Year/DOI: Proc. SPIE, Volume 7762, 77622E, (2010)
doi:10.1117/12.863610

A portable laser photostimulation and imaging microscope

Author(s): Volodymyr Nikolenko , Darcy S Peterka, Rafael Yuste

Abstract:

“We describe a compact microscope that uses a spatial light modulator (SLM) to control the excitation laser light. The flexibility of SLMs, which can mimic virtually any optical transfer function, enables the experimenter to create, in software, arbitrary spatio-temporal light patterns, including focusing and beam scanning, simply by calculating the appropriate phase mask. Our prototype, a scan-less device with no moving parts, can be used for laser imaging or photostimulation, supplanting the need for an elaborate optical setup. As a proof of principle, we generate complex excitation patterns on fluorescent samples and also perform functional imaging of neuronal activity in living brain slices.”

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Publication: Journal of Neural Engineering, (free download)

Issue/Year/DOI: J. Neural Eng., Volume 7, Number 4 (2010) 045001
doi: 10.1088/1741-2560/7/4/045001

Full 3D translational and rotational optical control of multiple rod-shaped bacteria

Author(s): Florian Hörner, Mike Woerdemann, Stephanie Müller, Berenike Maier, Cornelia Denz

Abstract:

“The class of rod-shaped bacteria is an important example of non-spherical objects where defined alignment is desired for the observation of intracellular processes or studies of the flagella. However, all available methods for orientational control of rod-shaped bacteria are either limited with respect to the accessible rotational axes or feasible angles or restricted to one single bacterium. In this paper we demonstrate a scheme to orientate rod-shaped bacteria with holographic optical tweezers (HOT) in any direction. While these bacteria have a strong preference to align along the direction of the incident laser beam, our scheme provides for the first time full rotational control of multiple bacteria with respect to any arbitrary axis. In combination with the translational control HOT inherently provide, this enables full control of all three translational and the two important rotational degrees of freedom of multiple rod-shaped bacteria and allows one to arrange them in any desired configuration.”

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Publication: Journal of Biophotonics, (subscription required)

Issue/Year/DOI: Journal of Biophotonics, Volume 3, Issue 7, pages 468–475, July 2010
DOI: 10.1002/jbio.201000033