A H Greenaway

Heriot-Watt University, Edinburgh, Scotland, United Kingdom

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Publications (53)70.28 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present the application of wavefront sensing to three-component, three-dimensional micro particle tracking velocimetry (μPTV). The technique is based upon examining the defocus of the wavefront scattered by a tracer particle and from such information establishing the 3-D tracer location. The imaging system incorporates a cylindrical lens acting as an anamorphic element that creates different magnifications in the two orthogonal axes. A single anamorphic image is obtained from each tracer, which contains sufficient information to reconstruct the wavefront defocus and uniquely identify the tracer’s axial position. A mathematical model of the optical system is developed and shows that the lateral and depth performance of the sensor can be largely independently varied across a wide range. Hence, 3-D image resolution can be achieved from a single viewpoint, using simple and inexpensive optics and applied to a wide variety of microfluidic or biological systems. Our initial results show that an uncertainty in depth of 0.18 μm was achieved over a 20-μm range. The technique was employed to measure the 3-D velocity field of micron-sized fluorescent tracers in a flow within a micro channel, and an uncertainty of 2.8 μm was obtained in the axial direction over a range of 500 μm. The experimental results were in agreement with the expected fluid flow when compared to the corresponding CFD model. Thus, wavefront sensing proved to be an effective approach to obtain quantitative measurements of three-component three-dimensional flows in microfluidic devices.
    Experiments in Fluids 01/2009; 47(4-5):849-863. · 1.57 Impact Factor
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    F. H. P. Spaan, A. H. Greenaway
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    ABSTRACT: Pupil replication and hypertelescope systems for imaging telluric exoplanets in scattered light are treated. Analytic expressions for the spread functions in one and two dimensions and in the presence of various forms of error are given. Error effects considered include aperture misalignment, tilts, piston, pointing errors, and unequal beam amplitude. The performance of the two approaches is contrasted, and the analytic results are compared with simulation results.
    The Astrophysical Journal 12/2008; 658(2):1380. · 6.73 Impact Factor
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    A. H. Greenaway, F. H. P. Spaan, and V. Mourai
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    ABSTRACT: Pupil replication is a new optical technique that decreases the diameter of the image of a star on the optical axis. With pupil replication, one can improve the suppression of starlight in high dynamic range exoplanet imaging and image planets closer to their host star. Pupil replication is an auxiliary technique intended to improve the imaging spectroscopic performance of coronographic or pupil apodization techniques. Here we introduce pupil replication and use numerical simulations to show that it may be combined with pupil apodization to improve exoplanet detection and spectroscopy.
    The Astrophysical Journal 12/2008; 618(2):L165. · 6.73 Impact Factor
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    ABSTRACT: We use a two-dimensional deformable mirror to shape the spatial profile of an ultrafast laser beam that is then used to inscribe structures in a soda-lime silica glass slide. By doing so we demonstrate that it is possible to control the asymmetry of the cross section of ultrafast laser inscribed optical waveguides via the curvature of the deformable mirror. When tested using 1.55 mum light, the optimum waveguide exhibited coupling losses of approximately 0.2 dB/facet to Corning SMF-28 single mode fiber and propagation losses of approximately 1.5 dB.cm(-1). This technique promises the possibility of combining rapid processing speeds with the ability to vary the waveguide cross section along its length.
    Optics Express 09/2008; 16(17):12786-93. · 3.55 Impact Factor
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    ABSTRACT: Observing biological processes in real-time and in single live cells is a vital step towards understanding cell behaviour and the way cells interact with the world around them, However, this requires real time three dimensional (4D) tracking of nanoparticles which is challenging and traditionally relies on sequential capture of 2D images to construct a 3D picture. We discuss a new approach to 4D nanoparticle tracking that utilises a specially designed diffraction grating which behaves as a lens with a different focal length in each diffraction order thereby producing pseudo D imaging over the imaged field. The current experimental system has the ability to track a single particle in a 50×50×6mum volume, with an accuracy of better than 50 nm in each dimension.
    01/2008;
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    ABSTRACT: We introduce an approach based on using an iterative simulated annealing algorithm to drive the outcome of femtosecond laser ablation towards a specific target shape by using a two-dimensional deformable mirror. Unlike previous work combining adaptive optics and laser machining we use the machining outcome itself as the fitness parameter for the optimization procedure. Single-pulse ablation features with programmable aspect ratios and dimensions as small as 2.5 µm are faithfully reproduced by the technique in a chromium-on-glass test sample.
    Journal of Optics A Pure and Applied Optics 01/2007; 9:1100-1104. · 1.92 Impact Factor
  • T. Huang, W. Lu, S. Zhang, A.H. Greenaway
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    ABSTRACT: We study an adaptive dynamical feedback system for phasing of segmented mirrors. The system, which combines a Zernike wave front sensor with a feedback loop, is shown to be capable of separating (static) misalignment errors of segmented mirrors from (dynamical) atmospheric turbulence. Our numerical simulations establish that it can retrieve multi-wave segment misalignment error in the presence of large-amplitude atmospheric phase distortion.
    Applied Physics B 12/2006; 86(1):139-145. · 1.78 Impact Factor
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    ABSTRACT: We present the application of wavefront sensing to particle image velocimetry for three-component (3C), three-dimensional (3D) flow measurement from a single view. The technique is based upon measuring the wavefront scattered by a tracer particle and from that wavefront the 3D tracer location can be determined. Hence, from a temporally resolved sequence of 3D particle locations the velocity vector field is obtained. Two approaches to capture the data required to measure the wavefronts are described: multi-planar imaging using a distorted diffraction grating and an anamorphic technique. Both techniques are optically efficient, robust and compatible with coherent and incoherent scattering from flow tracers. The depth (range) resolution and repeatability have been quantified experimentally using a single mode fiber source representing a tracer particle. The anamorphic approach is shown to have the greatest measurement range and hence was selected for the first proof of principle experiments using this technique for 3D particle imaging velocimetry (PIV) on a sparsely seeded gas phase flow.
    Experiments in Fluids 12/2006; 41(6):881-891. · 1.57 Impact Factor
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    ABSTRACT: A technique for coherent imaging based on spatial frequency heterodyning is described. Three images corresponding to three physical measurements are recorded. For the first measurement, a scene is simply illuminated with a coherent beam and for measurements 2 and 3, the scene is projected with cosine and sine fringes, respectively. Due to spatial frequency heterodyning, upper and lower side band information falls in the pass band of the imager. These bands are separated and correct phases and positions are assigned to these bands in the spatial frequency domain. An extension of bandwidth is achieved in the frequency domain and the inverse frequency domain data then give a high resolution coherent image.
    Chinese Optics Letters 03/2006; 4(3):148-151. · 1.07 Impact Factor
  • F. H. P. Spaan, E. Prot, V. Mourai, A. H. Greenaway
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    ABSTRACT: Pupil Replication is a technique which could be added to many existing high contrast imaging systems to improve the inner working angle or the contrast when using Pupil Replication. The output pupil of the telescope is replicated and mapped onto the input pupil of the high contrast imaging system. This decreases the size of the image of the star on axis and thereby increases the performance of the high contrast imaging system. In this paper the viability of such a system is assessed through mathematical analysis and simulations.
    EAS Publications Series 01/2006; 22:261-280.
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    H.I. Campbell, A.H. Greenaway
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    ABSTRACT: This paper provides an overview of wavefront sensing technologies. A brief background to the field of wavefront sensing is given, and several wavefront sensors are studied in detail. Particular attention is given to the Shack-Hartmann, Phase Diversity and Curvature wavefront sensors. Interferometric and Pyramid wavefront sensors are discussed as well as Schlieren imaging, algorithmic approaches (such as image sharpening), Shack-Hartmann Curvature hybrid wavefront sensing and modal wavefront sensors.
    EAS Publications Series 01/2006;
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    R El-Agmy, H Bulte, A H Greenaway, D Reid
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    ABSTRACT: We present a programmable beam-shaping method based on the combination of a deformable mirror membrane mirror and a simulated annealing algorithm. The algorithm iteratively adjusts the control voltages of 37 independent electrodes to reduce the variance between the chosen shape and the actual beam shape. The experimental results show that the system is capable of adaptively creating, on demand, Gaussian and super-Gaussian beam profiles that closely match the desired target parameters.
    Optics Express 09/2005; 13(16):6085-91. · 3.55 Impact Factor
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    ABSTRACT: High-resolution imaging can be achieved by optical aperture synthesis (OAS). Such an imaging process is subject to aberrations introduced by instrumental defects and/or turbulent media. Redundant spacings calibration (RSC) is a snapshot calibration technique that can be used to calibrate OAS arrays without use of assumptions about the object being imaged. Here we investigate the analogies between RSC and adaptive optics in passive imaging applications.
    Proc SPIE 01/2005;
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    A Mudassar, A R Harvey, A H Greenaway, J Jones
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    ABSTRACT: In this aperture synthesis three snapshots are required to synthesis the aperture: one is obtained with simple illumination of the scene, the second when the scene is projected with cosine fringes and the third with the fringes quadrature phase shifted. The spatial frequency of the fringes is set to twice the cut off frequency of the imager. Due to spatial frequency heterodyning bands of scene spatial frequencies lying both above and below the fringe spatial frequency are heterodyned simultaneously into the low-pass band of the imager Computer simulation results show extension of cut off frequency of the imager to three times the cut off frequency without aperture synthesis.
    Journal of Physics Conference Series 01/2005; 15(1).
  • R. M. El-Agmy, H. Bulte, A. H. Greenaway, D. T. Reid
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    ABSTRACT: We report programmable wavefront shaping using a high-resolution deformable mirror system and a wavefront sensor based on the phase diversity principle. Flattened, Gaussian and ridged wavefront shapes are demonstrated using a HeNe laser.
    Information Sciences - ISCI. 01/2005;
  • A.H. Greenaway, H.I. Campbell, S. Restaino
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    ABSTRACT: Phase-Diversity is an algorithm for reconstruction of wavefront phase from data corresponding to images of the input wavefront intensity on two planes normal to the direction of propagation and located at different positions along the axis of propagation. These planes are generally described as symmetrically placed about the image plane, but can equally well be symmetrically placed about the system input pupil. In this case the phase diversity algorithm becomes essentially the same as the wavefront curvature algorithm. For reconstruction of the wavefront phase the inverse problem is presented in terms of the di.erential Intensity Transport Equation and solved either iteratively or through use of Green’s functions. Here we will explore what other aberrations, other than defocus, can be used in a generalised phase diversity wavefront reconstruction. The possible advantages of this approach will be considered.
    12/2004: pages 177-186;
  • S. Zhang, H.I. Campbell, A.H. Greenaway
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    ABSTRACT: Some early results demonstrating the performance of the Generalised Phase Diversity Wavefront Sensor were presented. In these computer simulations we would seek to validate the theoretical analysis that we have previously published and to explore the optimisation of the sensor for various forms of wavefront error. Consideration would be given to the extent to which optimisation that exploits a priori information about the wavefront decreases the chance to detect other wavefront characteristics.
    12/2004: pages 187-196;
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    ABSTRACT: We describe an improved instrument for measuring at video rate (30 frames per second) the second-harmonic frequency-resolved optical gating trace of femtosecond pulses from a mode-locked laser oscillator. The system comprises separate scanning acquisition and pulse retrieval elements which together enable the exact pulse profile to be viewed in real time with a typical refresh rate of 1 Hz. Details are given of the optical system used, the electronic synchronization circuits and the acquisition and retrieval software employed. © 2003 American Institute of Physics.
    Review of Scientific Instruments 09/2003; · 1.60 Impact Factor
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    J Garduño-Mejía, A Greenaway, D Reid
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    ABSTRACT: We describe a femtosecond pulse shaper using a deformable membrane mirror. The pulses are measured with a real time second-harmonic-generation frequency-resolved optical gating system. Pulse shapes are modified according to a prescribed spectral phase. Accurate spectral phase design as well as pulse intensity modulation was achieved by using negative feedback mirror-surface control. Convergence to the chosen spectral phase design was typically achieved within several seconds.
    Optics Express 09/2003; 11(17):2030-40. · 3.55 Impact Factor
  • H. I. Campbell, A. H. Greenaway, S. R. Restaino
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    ABSTRACT: In this presentation we will explore the generalisation of the phase diversity approach, and show what properties the aberration function used should have in order to provide a sensor. We will show that this general approach offers scope for the implementation of adaptive optics systems that can be remarkably compact and in which the corrected image can be stored simultaneously with an estimate of residual wavefront errors averaged over the exposure time. We will consider the issues of data reduction using this generalised approach to reconstruct the input wavefront shape.
    01/2003;

Publication Stats

390 Citations
70.28 Total Impact Points

Institutions

  • 2000–2009
    • Heriot-Watt University
      • • School of Engineering and Physical Sciences
      • • Department of Physics
      Edinburgh, Scotland, United Kingdom
    • Hokkaido University
      • Division of Media and Network Technologies
      Sapporo-shi, Hokkaido, Japan
    • University of Bath
      • Department of Physics
      Bath, ENG, United Kingdom
  • 1996
    • The International Society for Optics and Photonics
      International Falls, Minnesota, United States