Quantitative Phase Contrast Imaging Research Articles

Quantitative phase contrast imaging of arborescent graft polystyrene by off-axis transmission electron holography

Imaging nanoscale polymer objects in the Transmission Electron Microscope is difficult, because small polymeric objects interact only weakly with intermediate-energy electrons. Heavy element staining can induce significant amplitude contrast, but stains can introduce artifacts that complicate the structure determination at nanometer length scales. This paper explores transmission electron holography for phase contrast imaging of unstained arborescent graft polystyrene nanoparticles. Holography is able to recover significant phase contrast from these particles despite the fact that there is negligible amplitude contrast. Comparative imaging experiments show that off-axis holography provides substantially higher contrast than that generated by the traditional method of transferring phase information to amplitude information via defocus. This effect is a consequence of different lens contrast-transfer behavior in each of these two imaging approaches. Under kinematical conditions when the appropriate mean inner potential is known, the specimen's projected thickness can be directly mapped from the holographic phase image to give a measure of the specimen's three-dimensional shape. Such quantitative imaging shows that individual arborescent graft polystyrene nanoparticles, which are spherical in a good solvent, adopt a flattened shape when deposited on a carbon substrate and allowed to dry.

Quantitative Phase Contrast Microscopy of Living Astrocytes By Numerical Reconstruction of Digital Holograms

We have developed a method of numerical holography which allows simultaneous intensity and quantitative phase contrast imaging. Measurement of optical path length provides precise information about the cell morphology. As presented in Fig. 1, the experimental set-up for the recording of digital holograms is basically a Mach-Zender interferometer. At the exit of the interferometer, a CCD camera records a hologram which is made by the interference between a reference wave R and the object wave O that is transmitted by the biological sample. In order to obtain a plane wave as reference, a beam expander (B.E.) including a pinhole is introduced in the reference arm and enlarges the beam diameter to about 2cm. A similar system which produces a smaller beam diameter (≈5mm) is inserted in the objet arm. To perform holography in the off-axis geometry, the mirror in the reference arm is oriented in such a way that the reference wave reaches the CCD camera with a small incidence angle.

Digital holography for quantitative phase-contrast imaging

We present a new application of digital holography for phase-contrast imaging and optical metrology. This holographic imaging technique uses a CCD camera for recording of a digital Fresnel off-axis hologram and a numerical method for hologram reconstruction. The method simultaneously provides an amplitude-contrast image and a quantitative phase-contrast image. An application to surface profilometry is presented and shows excellent agreement with contact-stylus probe measurements.

Hard x-ray quantitative non-interferometric phase-contrast microscopy

We report the results of quantitative phase-contrast imaging experiments using synchrotron radiation, in-line imaging geometry and a non-interferometric phase retrieval technique. This quantitative imaging method is fast, simple, robust, does not require sophisticated x-ray optical elements and can potentially provide submicron spatial resolution over a field of view of the order of centimetres. In the present experiment a spatial resolution of approximately 0.8 m has been achieved in images of a polystyrene sphere using 19.6 keV x-rays. We demonstrate that appropriate processing of phase-contrast images obtained in the in-line geometry can reveal important new information about the internal structure of weakly absorbing organic samples. We believe that this technique will also be useful in phase-contrast tomography.

On X-ray phase retrieval from polychromatic images

Methods for quantitative phase retrieval from polychromatic Fresnel-region images obtained at a fixed position along the optic axis are proposed. These methods eliminate the need for collecting images at multiple distances from the object, thus possibly simplifying the experimental procedure and allowing simultaneous recording of the image intensity data. Applications to hard X-ray in-line phase-contrast imaging with the use of conventional and energy-sensitive detectors are discussed. The suggested technique may also be applicable in quantitative phase-contrast imaging and tomography using radiation of other types than X-rays.