School of Physics - Research Publications

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Subject: Optics and Opto-electronic Physics ; Physical Sciences × Author: Nugent, Keith ×

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    Precision measurement of the electromagnetic fields in the focal region of a high-numerical-aperture lens using a tapered fiber probe
    Rhodes, SK ; Nugent, KA ; Roberts, A (OPTICAL SOC AMER, 2002-08)
    We present a measurement of the intensity around the focus of a N.A.-0.95 lens using a tapered optical fiber probe. An asymmetry introduced by the vector nature of the incident polarized light is evident, although it is inconsistent with that predicted theoretically by considering the magnitude squared of the electric field. The sensitivity of the probe to different components of the electromagnetic field is considered, and it is shown that the measurement is consistent with vector diffraction theory when the probe properties are taken into account.
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    Unique phase recovery for nonperiodic objects
    Nugent, KA ; Peele, AG ; Chapman, HN ; Mancuso, AP (AMERICAN PHYSICAL SOC, 2003-11-14)
    It is well known that the loss of phase information at detection means that a diffraction pattern may be consistent with a multitude of physically different structures. This Letter shows that it is possible to perform unique structural determination in the absence of a priori information using x-ray fields with phase curvature. We argue that significant phase curvature is already available using modern x-ray optics and we demonstrate an algorithm that allows the phase to be recovered uniquely and reliably.
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    Refractive index profiling of axially symmetric optical fibers: a new technique
    Ampem-Lassen, E ; Huntington, ST ; Dragomir, NM ; Nugent, KA ; Roberts, A (OPTICAL SOC AMER, 2005-05-02)
    We present a new technique for determining the refractive index profiles of axially symmetric optical fibers based on imaging phase gradients introduced into a transmitted optical field by a fiber sample. An image of the phase gradients within the field is obtained using a new non-interferometric technique based on bright field microscopy. This provides sufficient information to reconstruct the refractive index profile using the inverse Abel transform. The technique is robust, rapid and possesses high spatial resolution and we demonstrate its application to the reconstruction of the refractive index profiles of a single-mode and a multimode optical fiber.
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    X-ray phase contrast tomography with a bending magnet source
    Peele, AG ; De Carlo, F ; McMahon, PJ ; Dhal, BB ; Nugent, KA (AMER INST PHYSICS, 2005-08)
    X-ray radiography and x-ray tomography are important tools for noninvasive characterization of materials. Historically, the contrast mechanism used with these techniques has been absorption. However, for any given sample there are x-ray energies for which absorption contrast is poor. Alternatively, when good contrast can be obtained, radiation damage from an excessive dose may become an issue. Consequently, phase-contrast methods have in recent years been implemented at both synchrotron and laboratory facilities. A range of radiographic and tomographic demonstrations have now been made, typically utilizing the coherent flux from an insertion device at a synchrotron or a microfocus laboratory source. In this paper we demonstrate that useful results may be obtained using a bending magnet source at a synchrotron. In particular we show that the same beamline can be used to make and characterize a sample made by x-ray lithographic methods.