H. J. Kreuzer

Digital in-line holography for biological applications

Digital in-line holography with numerical reconstruction has been developed into a new tool, specifically for biological applications, that routinely achieves both lateral and depth resolution, at least at the micron level, in three-dimensional imaging. The experimental and numerical procedures have been incorporated into a program package with a very fast reconstruction algorithm that is now capable of real-time reconstruction. This capability is demonstrated for diverse objects, such as suspension of microspheres and biological samples (diatom, the head of Drosophila melanogaster), and the advantages are discussed by comparing holographic reconstructions with images taken by using conventional compound light microscopy.

Tracking particles in four dimensions with in-line holographic microscopy.

We describe a simple holographic method that has enabled us to capture as a single data set the trajectories of micrometer-sized objects suspended in water. By subtracting consecutive holograms of a particle suspension and then adding these difference holograms, we constructed a final data set that contains the time evolution of the particle trajectories free from spurious background interference effects. The method is illustrated by a recording of the motion of 5-10-microm diameter algae in water.

Digital in-line holography of microspheres.

We have used digital in-line holography (DIH) with numerical reconstruction to image micrometer-sized latex spheres as well as ferrimagnetic beads suspended in gelatin. We have examined in detail theoretically and experimentally the conditions necessary to achieve submicrometer resolution of holographic reconstructions. We found that both transparent and opaque particles could be imaged with a resolution that was limited only by the wavelength of the light used. Simple inspection of intensity profiles through a particle allowed an estimate to be made of the particles three position coordinates within an accuracy of a few hundred nanometers. When the derivative of a second-order polynomial fitted to the intensity profiles was taken, the X, Y, Z position coordinates of particles could be determined within +/-50 nm. More-accurate positional resolution should be possible with the help of more-advanced computer averaging techniques. Because a single hologram can give information about a large collection of distributed particles, DIH offers the prospect of a powerful new tool for three-dimensional tracking of particles.

First-principles theory of surface thermodynamics and kinetics

In this Letter, with the aim to improve upon this approach, we combine state-of-the-art procedures of (i) microscopic theories, i.e., DFT electronic structure calculations and (ii) macroscopic phenomenological approaches, i.e., lattice gas and rate equations, and Monte Carlo schemes. On doing this, we present a consistent first-principles-based approach for calculation of the thermodynamic and kinetic properties of an adsorbate, such as heats of adsorption, temperature programmed desorption (TPD) spectra, and the surface phase diagram. We have chosen the system of oxygen at Ru(0001) for which detailed structural [4 ‐9], thermodynamic [10], and kinetic data [11,12] exist. We will show that, with the present approach, a realistic description of these physical properties is indeed feasible.

Immersion digital in-line holographic microscopy.

Digital in-line holographic microscopy is a promising new tool for high resolution imaging. We demonstrate, by using latex beads, that a considerable increase in numerical aperture, and, therefore, resolution can be achieved if the space between a source and a CCD camera chip is filled with a high refractive index medium. The high refractive index medium implies a shorter effective wavelength so that submicrometer resolution can be obtained with laser light in the visible range.

Theory of the point source electron microscope

Abstract The theory of the point source electron microscope including multiple scattering events is formulated. Images are calculated and analyzed for carbon clusters, varbon fibers and large metal films. A Fourier-like transform is then shown to be appropriate for the reconstruction of the object with atomic resolution. Effects due to higher partial waves, multiple scattering and finite image size are examined in detail.

Submersible digital in-line holographic microscope

Few instruments exist that can image microscopic marine organisms in their natural environment so that their locomotion mechanisms, feeding habits, and interactions with surfaces, such as biofouling, can be investigated in situ. We describe here the design and performance of a simple submersible digital in-line holographic microscope that can image organisms and their motion with micron resolution and that can be deployed from small vessels. Holograms and reconstructed images of several microscopic aquatic organisms were successfully obtained down to a depth of 20m. Important microscope characteristics such as the effect of camera pixel size on lateral and depth resolutions as well as the maximum sample volume that can be imaged with a given resolution are discussed in detail.

Physics and chemistry in high electric fields

Abstract Theoretical progress is reviewed in our understanding of electrostatic fields at metal surfaces, of field-induced chemisorption of rare gases, and of the kinetics of thermal field desorption and field evaporation.

Swimming speed of three species of Alexandrium (Dinophyceae) as determined by digital in-line holography

N.I. Lewis, W. Xu, S.K. Jericho, H.J. Kreuzer, M.H. Jericho and A.D. Cembella. 2006. Swimming speed of three species of Alexandrium (Dinophyceae) as determined by digital in-line holography. Phycologia 45: 61–70. DOI: 10.2216/04-59.1 Digital in-line holographic (DIH) microscopy was used to track motility in several related species of the marine dinoflagellate Alexandrium in response to temperature after acclimation at selected temperatures. Numerical reconstruction of DIH holograms yielded high-contrast three-dimensional images of the trajectories of many motile cells swimming simultaneously throughout the sample volume. Swimming speed and trajectory were determined for clonal isolates of A. ostenfeldii, A. minutum and A. tamarense within the temperature range from 8 to 24°C. The strains of these species revealed differences in temperature optima for growth and tolerance that were a function of both acclimation responses and genetic factors reflecting the origin of the isolates. The fastest swimming speeds were recorded at 24°C for cells of A. minutum. Acclimated strains of all three species swam significantly slower at lower temperatures, although fastest swimming speeds did not always occur at temperature optima for growth. Aged cells from stationary phase cultures swam more slowly than cells in exponential growth phase. Doublets from a rapidly dividing culture swam faster than singlets from the same culture, confirming the propulsive advantage of paired cells. Holographic microscopy is a powerful tool for the acquisition of detailed observations of swimming behaviour of microalgal cells in the form of three-dimensional trajectories over the appropriate temporal (sub-second) and spatial (micrometer) scales.

ELECTROSTATIC FIELDS ABOVE INDIVIDUAL ATOMS

This review describes recent field ion microscopic measurements of local electrostatic fields in the immediate vicinity of individual surface atoms. The studies were stimulated and supported by self-consistent theoretical calculations on the field distribution close to single atoms of different electronic structure adsorbed on a metal surface in the presence of high external fields. The experimental and theoretical data establish the existence of strongly varying local field distributions above different surface atoms. New details concerning localized field ionization and image formation processes occurring in the field ion microscope are revealed.