Residue orbital angular momentum in interferenced double vortex beams with unequal topological charges

Author(s): S. H. Tao, X.-C. Yuan, J. Lin, and R. E. Burge

Abstract:

“When two vortex beams with unequal topological charges superpose coherently, orbital angular momentum (OAM) in the two beams would not be cancelled out completely in the interference. The residual OAMs contained by the superposed beam are located at different concentric rings and may have opposite orientations owing to the difference of the charges. The residual OAM can be confirmed by the rotation of microparticles when difference between the charges of two interfering beams is large.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 14, Issue 2, pp. 535-541, 2006
DOI: 10.1364/OPEX.14.000535

Dynamic closed-loop system for focus tracking using a spatial light modulator and a deformable membrane mirror

Author(s): Amanda J. Wright, Brett A. Patterson, Simon P. Poland, John M. Girkin, Graham M. Gibson, and Miles J. Padgett

Abstract:

“A dynamic closed-loop method for focus tracking using a spatial light modulator and a deformable membrane mirror within a confocal microscope is described. We report that it is possible to track defocus over a distance of up to 80 µm with an RMS precision of 57 nm. For demonstration purposes we concentrate on defocus, although in principle the method applies to any wavefront shape or aberration that can be successfully reproduced by the deformable membrane mirror and spatial light modulator, for example, spherical aberration.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 14, Issue 1, pp. 222-228, 2006
DOI: 10.1364/OPEX.14.000222

Collinear superposition of multiple helical beams generated by a single azimuthally modulated phase-only element

Author(s): J. Lin, X.-C. Yuan, S. H. Tao, and R. E. Burge

Abstract:

“We propose a highly efficient approach to generating multihelix beams that contain more than one helical mode, and the power distribution over helical modes is adjustable. A multihelix beam embedded with three collinear helical modes is demonstrated by use of a spatial light modulator.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 30, Issue 24, pp. 3266-3268, 2006
DOI: 10.1364/OL.30.003266

Fractional optical vortex beam induced rotation of particles

Author(s): S. Tao, X-C. Yuan, J. Lin, X. Peng, and H. Niu

Abstract:

“We experimentally demonstrate optical rotation and manipulation of microscopic particles by use of optical vortex beams with fractional topological charges, namely fractional optical vortex beams, which are coupled in an optical tweezers system. Like the vortex beams with integer topological charges, the fractional optical vortex beams are also capable of rotating particles induced by the transfer of orbital angular momentum. However, the unique radial opening (low-intensity gap) in the intensity ring encompassing the dark core, due to the fractional nature of the beam, hinders the rotation significantly. The fractional vortex beams orbital angular momentum and radial opening are exploited to guide and transport microscopic particles.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 13, Issue 20, pp. 7726-7731, 2005
DOI: 10.1364/OPEX.13.007726

Creating permanent 3D arrangements of isolated cells using holographic optical tweezers

Author(s): Pamela Jordan, Jonathan Leach, Miles Padgett, Paul Blackburn, Neil Isaacs, Mattias Goksör, Dag Hanstorp, Amanda Wright, John Girkin and Jonathan Cooper

Abstract:

“We report the creation of permanent 3D configurations of cells, at predefined positions, within a gelatin matrix. The technique used holographic optical tweezers to manipulate individual E. coli within a solution comprising monomer precursors. The matrix was then set and after the laser beam was removed, we were able to demonstrate that the structures remained intact for many days. We were also able to demonstrate that, in the presence of appropriate nutrients, the E. coli survived within the gelatin matrix for several days. The technique could have a number of potential future applications, including the arrangement of a variety of different cell types in complex architectures, as motifs for promoting tissue differentiation and growth within the field of cell engineering.”

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Publication: Lab on a Chip (free download)

Issue/Year/DOI: Lab Chip, 2005, 5, 1224-1228
DOI: 10.1039/b509218c

Raman imaging of floating cells

Author(s): Caitriona Creely, Giovanni Volpe, Gajendra Singh, Marta Soler, and Dmitri Petrov

Abstract:

“Raman imaging can yield spatially resolved biochemical information from living cells. To date there have been no Raman images published of cells in suspension because of the problem of immobilizing them suitably to acquire space-resolved spectra. In this paper in order to overcome this problem the use of holographic optical tweezers is proposed and implemented, and data is shown for spatially resolved Raman spectroscopy of a live cell in suspension.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 13, Issue 16, pp. 6105-6110, 2005
DOI: 10.1364/OPEX.13.006105

Shadow Effects in Spiral Phase Contrast Microscopy

Author(s): Alexander Jesacher, Severin Fürhapter, Stefan Bernet, and Monika Ritsch-Marte

Abstract:

“Recently it has been demonstrated that spatial filtering of images in microscopy with a spiral phase element in a Fourier plane of the optical path results in a strong edge enhancement of object structures. In principle the operation is isotropic, i.e., all phase edges of a sample object are highlighted simultaneously, independent of their local direction. However, here we demonstrate that the symmetry can be broken intentionally by controlling the phase of the central area of a spiral phase hologram, which is displayed at a computer controlled spatial light modulator. This produces an apparent shadow effect which can be rotated at video rate. The resulting relieflike impression of the sample topography with a longitudinal resolution in the subwavelength regime is demonstrated by imaging a standard low contrast test sample consisting of a human cheek cell.”

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Publication: Physical Review Letters
Issue/Year: Phys. Rev. Lett. 94, 233902 (2005)
DOI: 10.1103/PhysRevLett.94.233902

3D interferometric optical tweezers using a single spatial light modulator

Author(s): Ethan Schonbrun, Rafael Piestun, Pamela Jordan, Jon Cooper, Kurt Wulff, Johannes Courtial, and Miles Padgett

Abstract:

“Hexagonal arrays of micron sized silica beads have been trapped in three-dimensions within an optical lattice formed by the interference of multiple plane-waves. The optical lattice design with sharply peaked intensity gradients produces a stronger trapping force than the traditionally sinusoidal intensity distributions of other interferometric systems. The plane waves were generated using a single, phase-only, spatial light modulator (SLM), sited near a Talbot image plane of the traps. Compared to conventional optical tweezers, where the traps are formed in the Fourier-plane of the SLM, this approach may offer an advantage in the creation of large periodic array structures. This method of pattern formation may also be applicable to trapping arrays of atoms.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 13, Issue 10, pp. 3777-3786, 2006
DOI: 10.1364/OPEX.13.003777

Experimental demonstration of holographic three-dimensional light shaping using a Gerchberg–Saxton algorithm

Author(s): Graeme Whyte and Johannes Courtial

Abstract:

“We use a three-dimensional Gerchberg–Saxton algorithm (Shabtay (2003) Opt. Commun. 226 33) to calculate the Fourier-space representation of physically realizable light beams with arbitrarily shaped three-dimensional intensity distributions. From this representation we extract a phase-hologram pattern that allows us to create such light beams experimentally. We show several examples of experimentally shaped light beams.”

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Publication: New Journal of Physics
Issue/Year: New J. Phys. 7 117, 2005
DOI: 10.1088/1367-2630/7/1/117

Dynamic optical manipulation using intensity patterns directly projected by a reflective spatial light modulator

Author(s): S. H. Tao, X.-C. Yuan, H. B. Niu and X. Peng

Abstract:

“We propose a simple method to manipulate microparticles dynamically with intensity-modulated patterns projected by a spatial light modulator (SLM), on which the patterns are controlled by a computer directly. The patterns are intensity–intensity modulated by the SLM without involving any computation or algorithm. With the dynamic patterns we can manipulate particles interactively and visibly by drawing or mouse-dragging pictures or even playing a video file on the computer screen. Experimental observations verified the feasibility of the proposed technique as a simple and direct solution for interactive optical manipulation.”

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Publication: Review of Scientific Instruments
Issue/Year: Rev. Sci. Instrum. 76, 056103 (2005)
DOI: 10.1063/1.1898065