Simulating newborn face perception.

A frequently asked question concerns what a newborn infant can actually see. The contrast sensitivity function of newborn infants is well known, but its implications for the ability of newborns to perceive faces of adults remain unclear. We filtered gray scale animations of facial expressions in terms of both spatial frequency and contrast to correspond to the properties of newborn infants' acuity and showed them to adult participants. We reasoned that if adults were unable to identify the depicted facial expressions, then it would also seem unlikely that newborn infants could identify the same expressions. We found that for the simulated acuity the different expressions could be rather well identified at a distance of 30 cm, but when the distance was increased to 120 cm their discriminability was much degraded. This shows that although the perception of faces and facial expressions can function at the low visual resolution of the newborn infant, it is insufficient for distinguishing faces and facial expressions at moderate distances.

Imaging of vascular smooth muscle cells with soft X-ray spectromicroscopy.

Using X-ray microscopy and spectromicroscopy, vascular smooth muscle cells (VSMCs) were imaged, prepared without using additional embedding material or staining, but by applying simple, noncryo fixation techniques. The cells were imaged with a compact source transmission X-ray microscope and a scanning transmission X-ray microscope (STXM). With the STXM, spectromicroscopy was performed at the C K-edge and the Ca L(III,II)-edges. VSMCs were chosen because of their high amount of actin stress fibers, so that the actin cytoskeleton should be visible. Other parts of the cell, such as the nucleus and organelles, were also identified from the micrographs. Both in the spectra and the images, the effects of the different preparation procedures were observable. Furthermore, Ca hotspots were detected and their density is determined.

Numerical model for tomographic image formation in transmission x-ray microscopy.

We present a numerical image-formation model for investigating the influence of partial coherence, sample thickness and depth-of-focus on the accuracy of tomographic reconstructions in transmission x-ray microscopes. The model combines wave propagation through the object by finite difference techniques with Fourier methods. We include a ray-tracing model to analyse the origin of detrimental stray light in zone plate-based x-ray microscopes. These models allow optimization of x-ray microscopy systems for quantitative tomographic imaging of thick objects. Results show that both the depth-of-focus and the reconstructed local absorption coefficient are highly dependent on the degree of coherence of the optical system.

Laboratory soft-x-ray microscope for cryotomography of biological specimens.

Soft-x-ray cryotomography allows quantitative and high-resolution three-dimensional imaging of intact unstained cells. To date, the method relies on synchrotron-radiation sources, which limits accessibility for researchers. Here we present a laboratory water-window microscope for cryotomography. It is based on a λ=2.48 nm liquid-jet laser-plasma source, a normal-incidence multilayer condenser, a 30 nm zone-plate objective, and a cryotilt sample holder. We demonstrate high-resolution imaging, as well as quantitative tomographic imaging, of frozen intact cells. The reconstructed tomogram of the intracellular local absorption coefficient shows details down to ∼100 nm.

Sub-25-nm laboratory x-ray microscopy using a compound Fresnel zone plate.

Improving the resolution in x-ray microscopes is of high priority to enable future applications in nanoscience. However, high-resolution zone-plate optics often have low efficiency, which makes implementation in laboratory microscopes difficult. We present a laboratory x-ray microscope based on a compound zone plate. The compound zone plate utilizes multiple diffraction orders to achieve high resolution while maintaining reasonable efficiency. We analyze the illumination conditions necessary for this type of optics in order to suppress stray light and demonstrate microscopic imaging resolving 25 nm features.

High-resolution computed tomography with a compact soft x-ray microscope.

Computed tomography based on high-resolution soft x-ray microscopy utilizes the natural contrast for biological specimens provided by the water window (lambda = 2.4 - 4.4 nm) and the high resolving power of zone plate objectives. It is capable of revealing the 3D structure of biological specimens at sub-visible-microscopic resolution. To date, the technique has only been available at synchrotron-based microscopes, which limits the researchers access. In the present paper we demonstrate high-resolution soft x-ray tomography with a laboratory zone-plate-based soft x-ray microscope. The specimen, a diatom mounted on a glass capillary, was reconstructed from a tilt series of 53 images covering 180 degrees using a filtered back projection algorithm. The resolution of the tomogram was estimated to a half period of 140 nm using a differential-phase-residual method. Cryo-fixation, increased source brightness and extended-depth-of-focus objectives are important for pushing the resolution of compact systems for biological samples.

Theoretical development of a high-resolution differential-interference-contrast optic for x-ray microscopy.

In this paper, the theoretical background and development of a differential-interference contrast (DIC) x-ray optic is presented. The single-element optic is capable of high-resolution phase contrast imaging and is compatible with compact sources. It is shown that an understanding of the coherence requirements in this type of imaging is imperative and is explained in detail. The optic is capable of a wavefront separation equal to the resolution of the optic which places only minor constraints on the object illumination.

Simulation of partially coherent image formation in a compact soft X-ray microscope.

In this paper, we describe a numerical method of simulating two-dimensional images in a compact soft X-ray microscope using partially coherent illumination considerations. The work was motivated by recent test object images obtained by the latest generation in-house compact soft X-ray microscope, which showed diffraction-like artifacts not observed previously. The numerical model approximates the condenser zone plate as a secondary incoherent source represented by individually coherent but mutually incoherent source points, each giving rise to a separate image. A final image is obtained by adding up all the individual source point contributions. The results are compared with the microscope images and show qualitative agreement, indicating that the observed effects are caused by partially coherent illumination.