Keith A. Nugent

Quantitative optical phase microscopy.

We present a new method for the extraction of quantitative phase data from microscopic phase samples by use of partially coherent illumination and an ordinary transmission microscope. The technique produces quantitative images of the phase profile of the sample without phase unwrapping. The technique is able to recover phase even in the presence of amplitude modulation, making it significantly more powerful than existing methods of phase microscopy. We demonstrate the technique by providing quantitatively correct phase images of well-characterized test samples and show that the results obtained for more-complex samples correlate with structures observed with Nomarski differential interference contrast techniques.

Coherent methods in the X-ray sciences

X-ray sources are developing rapidly and their coherent output is growing correspondingly. The increased coherent flux from modern X-ray sources is being matched with an associated development in experimental methods. This article reviews the literature describing the ideas that utilize the increased brilliance from modern X-ray sources. It explores how ideas in coherent X-ray science are leading to developments in other areas, and vice versa. The article describes measurements of coherence properties and uses this discussion as a base from which to describe partially coherent diffraction and X-ray phase-contrast imaging, with applications in materials science, engineering and medicine. Coherent diffraction imaging methods are reviewed along with associated experiments in materials science. Proposals for experiments to be performed with the new X-ray free-electron lasers are briefly discussed. The literature on X-ray photon-correlation spectroscopy is described and the features it has in common with other coherent X-ray methods are identified. Many of the ideas used in the coherent X-ray literature have their origins in the optical and electron communities and these connections are explored. A review of the areas in which ideas from coherent X-ray methods are contributing to methods for the neutron, electron and optical communities is presented.

Thermal stability and relaxation in diamond-like-carbon. A Raman study of films with different sp3 fractions (ta-C to a-C)

The thermal stability and relaxation processes in hydrogen free diamond-like-carbon films with different sp3 fractions (40%, 60%, and 80%) are comparatively studied for the first time by visible Raman spectroscopy. The 80% sp3 film is very stable under annealing in the entire temperature region investigated (300–1270 K) and shows only a minor change of the optical transmission, most likely due to a mild sp2 clustering, but no graphitization. This is very important for practical applications requiring a high thermal stability. The films with lower sp3 fraction show a thermal stability which decreases with the decreasing sp3. Graphitization starts at 700 K for the 40% sp3 film.

Refractive Index Measurement in Viable Cells Using Quantitative Phase-Amplitude Microscopy and Confocal Microscopy

The refractive index (RI) of cellular material provides fundamental biophysical information about the composition and organizational structure of cells. Efforts to describe the refractive properties of cells have been significantly impeded by the experimental difficulties encountered in measuring viable cell RI. In this report we describe a procedure for the application of quantitative phase microscopy in conjunction with confocal microscopy to measure the RI of a cultured muscle cell specimen.

Quantitative phase-amplitude microscopy I: optical microscopy

In this paper, the application of a new optical microscopy method (quantitative phase‐amplitude microscopy) to biological imaging is explored, and the issue of resolution and image quality is examined. The paper begins by presenting a theoretical analysis of the method using the optical transfer function formalism of Streibl (1985 ). The effect of coherence on the formation of the phase image is explored, and it is shown that the resolution of the method is not compromised over that of a conventional bright‐field image. It is shown that the signal‐to‐noise ratio of the phase recovery, however, does depend on the degree of coherence in the illumination.

PHASE RETRIEVAL WITH THE TRANSPORT-OF-INTENSITY EQUATION. II. ORTHOGONAL SERIES SOLUTION FOR NONUNIFORM ILLUMINATION

In a previous paper [ J. Opt. Soc. Am. A12, 1932 ( 1995)] we presented a method for phase recovery with the transport-of-intensity equation by use of a series expansion. Here we develop a different method for the solution of this equation, which allows recovery of the phase in the case of nonuniform illumination. Though also based on the orthogonal series expansion, the new method does not require any separate boundary conditions and can be more easily adjusted for apertures of various shapes. The discussion is primarily for the case of a circular aperture and Zernike polynomials, but we also outline the solution for a rectangular aperture and Fourier harmonics. The latter example may have some substantial advantages, given the availability of the fast Fourier transform.

Rapid quantitative phase imaging using the transport of intensity equation

Abstract A method for digital phase imaging is proposed. It requires the measurement of intensity in two adjacent planes orthogonal to the optical axis. The phase is subsequently recovered by a Fast Fourier Transform of the Transport of Intensity Equation. The algorithm can be used when the illuminating beam has an arbitrary intensity distribution and is limited by a rectangular aperture. The phase retrieval formulae take on an especially simple and numerically efficient form in the case of uniform illumination. Several simulated examples are presented to confirm the viability of the algorithm.

Quantitative phase-sensitive imaging in a transmission electron microscope

This paper presents a new technique for forming quantitative phase and amplitude electron images applicable to a conventional transmission electron microscope. With magnetised cobalt microstructures used as a test object, we use electron holography to obtain an independent measurement of the phase shift. After a suitable calibration of the microscope, we obtain quantitative agreement of the phase shift imposed on the 200 keV electrons passing through the sample.

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.

Quantitative phase tomography

We describe the application of a new technique for the simultaneous determination of three-dimensional absorption and refractive index distributions using a combination of quantitative phase-amplitude microscopy and tomographic reconstruction techniques. We briefly review the phase-amplitude microscopy technique and present experimental results in which we have successfully reconstructed the refractive index profile of two different optical fibres.