A. J. Wright

University of Strathclyde, Glasgow, SCT, United Kingdom

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Publications (12)33.66 Total impact

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    ABSTRACT: We contrast the two situations in which either a light beam is incident on a moving medium or a moving optical image is incident on a stationary medium. The principle of relativity suggests that the effects on the light of propagating through the medium should be similar. We find, however, that there are subtle differences which we can understand in terms of the relative alignment of the Poynting and wave vectors. Our analysis and experiments investigate both translational motion and rotation.
    Physical Review Letters 04/2008; 100(15):153902. · 7.73 Impact Factor
  • S P Poland, A J Wright, J M Girkin
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    ABSTRACT: A significant challenge for in vivo imaging is to remove movement artifacts. These movements (typically due to either respiration and cardiac-related movement or surface chemical response) are normally limited to the axial direction, and hence features move in and out of the focal plane. This presents a real problem for high-resolution optically sectioned imaging techniques such as confocal and multiphoton microscopy. To overcome this we have developed an actively locked focus-tracking system based around a deformable membrane mirror. This has a significant advantage over more conventional focus-tracking techniques where the microscope objective is dithered, since the active element is not in direct, or indirect, contact with the sample. To examine the operational limits and to demonstrate possible applications for this form of focus locking, sample oscillation and movement are simulated for two different biological applications. We were able to track focus over a 400 microm range (limited by the range of the piezomounted objective) with a rms precision on the focal depth of 0.31 microm +/- 0.05 microm.
    Optics Letters 04/2008; 33(5):419-21. · 3.39 Impact Factor
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    ABSTRACT: We report on a practical method for the implementation of Adaptive Optics in optical sectioning microscopy to remove system and sample induced aberrations. Correcting for induced aberrations on a pixel-by-pixel basis would take in excess of 4 minutes and greatly increase the risk of sample damage due to photo-bleaching and photo-toxicity; this is clearly an impractical approach. We show that a single aberration correction per optical slice is adequate to significantly improve the image quality across the whole field of view. We present results illustrating the success of this method for a sample scanning and beam scanning system using confocal and multiphoton microscopy.
    01/2008;
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    ABSTRACT: We report the use of adaptive optics with coherent anti-Stokes Raman scattering (CARS) microscopy for label-free deep tissue imaging based on molecular vibrational spectroscopy. The setup employs a deformable membrane mirror and a random search optimization algorithm to improve signal intensity and image quality at large sample depths. We demonstrate the ability to correct for both system and sample-induced aberrations in test samples as well as in muscle tissue in order to enhance the CARS signal. The combined system and sample-induced aberration correction increased the signal by an average factor of approximately 3x for the test samples at a depth of 700 microm and approximately 6x for muscle tissue at a depth of 260 microm. The enhanced signal and higher penetration depth offered by adaptive optics will augment CARS microscopy as an in vivo and in situ biomedical imaging modality.
    Optics Express 01/2008; 15(26):18209-19. · 3.55 Impact Factor
  • S. P. Poland, A. J. Wright, J. M. Girkin
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    ABSTRACT: A significant challenge for in vivo imaging is to remove movement artifacts. These movements, (typically due to either respiration, cardiac related movement or surface chemical response) are normally limited to the axial direction and hence features move in and out of the focal plane. This presents a real problem for optically sectioned imaging techniques such as confocal and multiphoton microscopy. To overcome this we have developed an actively locked focus tracking system based around a deformable membrane mirror (DMM). This has significant advantages over more conventional systems as the active optical element is not in direct, or indirect, contact with the sample. In order to examine the operational limits and to demonstrate possible applications for this form of focus-locking sample oscillation and movement was simulated.
    01/2008;
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    ABSTRACT: The Brownian dynamics of an optically trapped water droplet is investigated across the transition from over to under-damped oscillations. The spectrum of position fluctuations evolves from a Lorentzian shape typical of overdamped systems (beads in liquid solvents), to a damped harmonic oscillator spectrum showing a resonance peak. In this later under-damped regime, we excite parametric resonance by periodically modulating the trapping power at twice the resonant frequency. We also derive from Langevin dynamics an explicit numerical recipe for the fast computation of the power spectra of a Brownian parametric oscillator. The obtained numerical predictions are in excellent agreement with the experimental data.
    Proc SPIE 09/2007;
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    ABSTRACT: We propose a versatile optical ring lattice suitable for trapping cold and quantum degenerate atomic samples. We demonstrate the realisation of intensity patterns from pairs of Laguerre-Gauss (exp(i??) modes with different ? indices. These patterns can be rotated by introducing a frequency shift between the modes. We can generate bright ring lattices for trapping atoms in red-detuned light, and dark ring lattices suitable for trapping atoms with minimal heating in the optical vortices of blue-detuned light. The lattice sites can be joined to form a uniform ring trap, making it ideal for studying persistent currents and the Mott insulator transition in a ring geometry.
    Optics Express 08/2007; 15(14):8619-25. · 3.55 Impact Factor
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    ABSTRACT: The Brownian dynamics of an optically trapped water droplet are investigated across the transition from over- to underdamped oscillations. The spectrum of position fluctuations evolves from a Lorentzian shape typical of overdamped systems (beads in liquid solvents) to a damped harmonic oscillator spectrum showing a resonance peak. In this later underdamped regime, we excite parametric resonance by periodically modulating the trapping power at twice the resonant frequency. The power spectra of position fluctuations are in excellent agreement with the obtained analytical solutions of a parametrically modulated Langevin equation.
    Physical Review Letters 08/2007; 99(1):010601. · 7.73 Impact Factor
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    Physical Review Letters 07/2007; 99(2). · 7.73 Impact Factor
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    ABSTRACT: Sample induced optical aberrations in slices of rat brain tissue have been corrected with a deformable membrane mirror. The aberration correction required by the DMM was determined using a genetic algorithm with the intensity at a point in the sample as a fitness value. We show that by optimising on the intensity of a single point in the sample we are able to improve the axial resolution across the whole field of view of the image at a fixed sample depth. The ratio between the corrected axial resolution and the diffraction limited resolution is on average 2.7 for a 50 µm thick rat brain tissue sample and 12 for a 380 µm thick sample across the whole field of view. The uncorrected ratio being 4.1 and 15.5 respectively. Using a single aberration correction per depth, compared to a point-by-point aberration correction, will significantly decrease scan times and therefore reduce photobleaching and phototoxic effects enabling more rapid microscopy with active aberration correction.
    Proc SPIE 03/2007;
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    ABSTRACT: We review recent developments in photonics research at Strathclyde University motivated by applications in biomedicine. Areas covered include novel sources for microscopy, micro-pixellated light emitting diodes, microlasers and microoptics.
    Lasers and Electro-Optics Society, 2005. LEOS 2005. The 18th Annual Meeting of the IEEE; 11/2005
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    ABSTRACT: Confocal techniques allow the user to achieve optically sectioned images with significantly enhanced axial and improved lateral resolution compared to widefield methods. Unfortunately, as one images more deeply within a sample, sample induced aberrations lead to a significant reduction in image resolution and contrast. Using adaptive optic techniques, we report on the effectiveness of a number of algorithms for removing sample induced aberrations. The viability and efficiency at a number of fitness parameters used in the optimisation routines is also considered.
    Proc SPIE 01/2005;