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Publication History View all

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    ABSTRACT: The linear Doppler shift is widely used to infer the velocity of approaching objects, but this shift does not detect rotation. By analyzing the orbital angular momentum of the light scattered from a spinning object, we observed a frequency shift proportional to product of the rotation frequency of the object and the orbital angular momentum of the light. This rotational frequency shift was still present when the angular momentum vector was parallel to the observation direction. The multiplicative enhancement of the frequency shift may have applications for the remote detection of rotating bodies in both terrestrial and astronomical settings.
    Science 08/2013; 341(6145):537-40.
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    ABSTRACT: In all space-borne laser interferometric gravitational wave detectors, inevitable differences in the lengths of the interferometer arms will potentially allow laser frequency noise to give rise to apparent gravitational wave signals. Active frequency stabilisation to a reference optical cavity and use of a frequency noise correction algorithm are both required to allow the target gravitational wave sensitivity to be achieved. Here we report on an experiment to frequency stabilise a laser over timescales of several hours, and to measure the excess noise using an independent analysing cavity. The residual frequency noise, at the spectral frequencies of interest to LISA, is shown to be significantly above the desired specification. However, in this relatively simple experiment it appears that the residual frequency noise can largely be accounted for by thermal drifts in the frequency discriminator cavity pathlength. Thermal stabilisation of the reference cavity can be expected to yeild a major improvement in absolute laser stability.
    Advances in Space Research 07/2013;
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    ABSTRACT: We derive reliable entanglement witnesses for coarse-grained measurements on continuous variable systems. These witnesses never return a "false positive" for identification of entanglement, under any degree of coarse graining. We show that even in the case of Gaussian states, entanglement witnesses based on the Shannon entropy can outperform those based on variances. We apply our results to experimental identification of spatial entanglement of photon pairs.
    Physical Review Letters 05/2013; 110(21):210502.
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    ABSTRACT: We present a technique to measure the velocity and flow profiles of a nanofluid in a microfluidic channel. Importantly, we extract the flow velocity from a series of standard brightfield images without employing particle tracking or laser-enhanced methods. Our analysis retrieves the flow information from the image structure function of sub-diffraction limited nanoparticles in suspension. We are able to spatially resolve the flow velocity and map out the parabolic flow profile across the width of a microfluidic channel.
    Lab on a Chip 05/2013; 13:2359.
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    ABSTRACT: Diamond anvil cells allow the behavior of materials to be studied at pressures up to hundreds of gigapascals in a small and convenient instrument. However, physical access to the sample is impossible once it is pressurized. We show that optical tweezers can be used to hold and manipulate particles in such a cell, confining micron-sized transparent beads in the focus of a laser beam. Here, we use a modified optical tweezers geometry, allowing us to trap through an objective lens with a higher working distance, overcoming the constraints imposed by the limited angular acceptance of the anvil cell. We demonstrate the effectiveness of the technique by measuring water's viscosity at pressures of up to 1.3 GPa. In contrast to previous viscosity measurements in anvil cells, our technique measures absolute viscosity and does not require scaling to the accepted value at atmospheric pressure. This method could also measure the frequency dependence of viscosity as well as being sensitive to anisotropy in the medium's viscosity.
    Physical Review Letters 03/2013; 110(9):095902.
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    ABSTRACT: Highly efficient and position sensitive photon detection is essential in a variety of applications from particle identification in fundamental nuclear and particle physics research, to radionuclide imaging in healthcare. Due to their position sensitivity and high packing fraction, the Hamamatsu H8500 and H9500 multianode photomultiplier tubes (MAPMTs) are promising candidates for such applications and have thus been studied through precision laser scans at several light intensities. This has revealed signal and crosstalk dependencies upon constructional features of the MAPMTs. Both MAPMTs feature a common last dynode output signal, which can be used for self-triggering. The strength and timing of this signal have been investigated for the H8500 MAPMT, yielding similar dependencies upon MAPMT construction and standard deviation time resolutions of 67.5 ps and 154.4 ps for 20 and single photoelectron signals respectively.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 12/2012; 695:326–329.
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    ABSTRACT: Go with the flow: Laser-induced flow patterns are used to direct the self-assembly of dissolved inorganic polyoxometalate clusters into robust, hollow tubular networks and micro-materials (see picture; scale bar: 500 μm) in real time. The hollow nature of these materials can be exploited to develop devices in which the self-assembled tubes act as microscopic flow channels.
    Angewandte Chemie International Edition 11/2012;
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    ABSTRACT: Holographic optical tweezers have found many applications including the construction of complex micron-scale 3D structures and the control of tools and probes for position, force, and viscosity measurement. We have developed a compact, stable, holographic optical tweezers instrument which can be easily transported and is compatible with a wide range of microscopy techniques, making it a valuable tool for collaborative research. The instrument measures approximately 30×30×35 cm and is designed around a custom inverted microscope, incorporating a fibre laser operating at 1070 nm. We designed the control software to be easily accessible for the non-specialist, and have further improved its ease of use with a multi-touch iPad interface. A high-speed camera allows multiple trapped objects to be tracked simultaneously. We demonstrate that the compact instrument is stable to 0.5 nm for a 10 s measurement time by plotting the Allan variance of the measured position of a trapped 2 μm silica bead. We also present a range of objects that have been successfully manipulated.
    The Review of scientific instruments 11/2012; 83(11):113107.
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    ABSTRACT: Pairs of planar ray-rotating windows can rotate the view through different angles. The angle by which an object appears rotated is independent of the distance of the object behind the windows. The observer distance has to be chosen such that the observer is in a principal plane of this combination of windows.
    Optics Communications 11/2012; 285(24):4802–4806.
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    ABSTRACT: Autostereograms, or “Magic Eye” pictures, are repeating patterns designed to give the illusion of depth. Here we discuss optical resonators that create light patterns which, when viewed from a suitable position by a monocular observer, are autostereograms of the three-dimensional shape of one of the mirror surfaces.
    Optics Communications 09/2012; 285(19):3971–3975.
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