P. J. McMahon

Quantitative phase-amplitude microscopy. III. The effects of noise.

We explore the effect of noise on images obtained using quantitative phase‐amplitude microscopy – a new microscopy technique based on the determination of phase from the intensity evolution of propagating radiation. We compare the predictions with experimental results and also propose an approach that allows good‐quality quantitative phase retrieval to be obtained even for very noisy data.

Imaging: Phase radiography with neutrons

The interaction of neutrons with matter enables neutron radiography to complement X-ray radiography in analysing materials. Here we describe a simple quantitative method that provides a new contrast mechanism for neutron radiography and allows samples to be imaged at low radiation doses. Large phase shifts can be measured accurately from detailed structures not amenable to conventional techniques.

Spatial coherence measurement of X-ray undulator radiation

We measure the spatial coherence function of a quasi-monochromatic 1.1 keV X-ray beam from an undulator at a third-generation synchrotron. We use a Youngs slit apparatus to measure the coherence function and find that the coherence measured is poorer than expected. We show that this difference may be attributed to the effects of speckle due to the beamline optics. The conditions for successful coherence transport are considered.

Noninterferometric quantitative phase imaging with soft x rays.

We demonstrate quantitative noninterferometric x-ray phase-amplitude measurement. We present results from two experimental geometries. The first geometry uses x rays diverging from a point source to produce high-resolution holograms of submicrometer-sized objects. The measured phase of the projected image agrees with the geometrically determined phase to within +/-7%. The second geometry uses a direct imaging microscope setup that allows the formation of a magnified image with a zone-plate lens. Here a direct measure of the object phase is made and agrees with that of the magnified object to better than +/-10%. In both cases the accuracy of the phase is limited by the pixel resolution.

Phase radiography with neutrons.

The interaction of neutrons with matter enables neutron radiography to complement X-ray radiography in analysing materials. Here we describe a simple quantitative method that provides a new contrast mechanism for neutron radiography and allows samples to be imaged at low radiation doses. Large phase shifts can be measured accurately from detailed structures not amenable to conventional techniques.

Quantitative X-ray phase tomography with sub-micron resolution

Tomographic X-ray phase reconstructions of an atomic force microscope tip with a spatial resolution of better than 900 nm are presented. The data was acquired using an X-ray energy of 1.83 keV using a zone plate based microscope at a third generation synchrotron, the Advanced Photon Source at the Argonne National Laboratory. The phase tomographic data is quantitatively accurate and we confirm that the deduced refractive index is in agreement with the known properties of the sample. Our results open the way for full 3D imaging of the complex refractive index with sub-micron spatial resolution.

X-ray tomographic imaging of the complex refractive index.

We present a quantitative three-dimensional reconstruction of the complex refractive index of boron clad tungsten fiber using 35 keV x rays. The reconstruction provides a quantitatively accurate measurement with a three-dimensional spatial resolution of approximately 2 μm.

X-ray phase contrast tomography with a bending magnet source

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.

Quantitative phase-amplitude microscopy II: differential interference contrast imaging for biological TEM.

Although phase contrast microscopy is widespread in optical microscopy, it has not been as widely adopted in transmission electron microscopy (TEM), which has therefore to a large extent relied on staining techniques to yield sufficient contrast. Those methods of phase contrast that are used in biological electron microscopy have been limited by factors such as the need for small phase shifts in very thin samples, the requirement for difficult experimental conditions, or the use of complex data analysis methods. We here demonstrate a simple method for quantitative TEM phase microscopy that is suitable for large phase shifts and requires only two images. We present a TEM phase image of unstained Radula sp. (liverwort spore). We show how the image may be transformed into the differential interference contrast image format familiar from optical microscopy. The phase images contain features not visible with the other imaging modalities. The resulting technique should permit phase contrast TEM to be performed almost as readily as phase contrast optical microscopy.

The detection and sizing of flaws in components from the hot-end of gas turbines using phase-contrast radiography with neutrons: a feasibility study

In this paper we present a feasibility study of the use of phase contrast radiography in the examination of components from the hot-section of gas turbine engines. These components are usually made from dense materials (nickel or cobalt based superalloys) and, consequently, radiographic examination requires either high energy X-rays (above 60 keV) or neutrons. The relative merits of employing X-rays and neutrons for phase contrast radiography are compared. It is shown that, for similar penetration, neutrons offer better sensitivity and that it should be possible to detect even micron-wide cracks orientated perpendicular to the incident rays. Simulation shows that, for cracks parallel to the incident rays, crack growth in increments of microns can be resolved by monitoring the development of the Fresnel diffraction pattern. Some preliminary experimental results are also presented that demonstrate an improvement over conventional neutron radiography.