FLUTE: a versatile linac-based THz source.

A new compact versatile linear accelerator named FLUTE is currently being designed at the Karlsruhe Institute of Technology. This paper presents the status of this 42 MeV machine. It will be used to generate strong (several 100 MV/m) ultra-short (~1 ps) THz pulses (up to ~4-25 THz) for photon science experiments, as well as to conduct a variety of accelerator studies. The latter range from comparing different coherent THz radiation generation schemes to compressing electron bunches and studying the electron beam stability. The bunch charge will cover a wide range (~100 pC-3 nC). Later we plan to also produce ultra-short x-ray pulses from the electron bunches, which, for example, could then be combined for THz pump-x-ray probe experiments.

Biochemical label-free tissue imaging with subcellular-resolution synchrotron FTIR with focal plane array detector.

The critical questions into the cause of neural degeneration, in Alzheimer disease and other neurodegenerative disorders, are closely related to the question of why certain neurons survive. Answers require detailed understanding of biochemical changes in single cells. Fourier transform infrared microspectroscopy is an excellent tool for biomolecular imaging in situ, but resolution is limited. The mid-infrared beamline IRENI (InfraRed ENvironmental Imaging) at the Synchrotron Radiation Center, University of Wisconsin-Madison, enables label-free subcellular imaging and biochemical analysis of neurons with an increase of two orders of magnitude in pixel spacing over current systems. With IRENI's capabilities, it is now possible to study changes in individual neurons in situ, and to characterize their surroundings, using only the biochemical signatures of naturally-occurring components in unstained, unfixed tissue. We present examples of analyses of brain from two transgenic mouse models of Alzheimer disease (TgCRND8 and 3xTg) that exhibit different features of pathogenesis. Data processing on spectral features for nuclei reveals individual hippocampal neurons, and neurons located in the proximity of amyloid plaque in TgCRND8 mouse. Elevated lipids are detected surrounding and, for the first time, within the dense core of amyloid plaques, offering support for inflammatory and aggregation roles. Analysis of saturated and unsaturated fatty acid ester content in retina allows characterization of neuronal layers. IRENI images also reveal spatially-resolved data with unprecedented clarity and distinct spectral variation, from sub-regions including photoreceptors, neuronal cell bodies and synapses in sections of mouse retina. Biochemical composition of retinal layers can be used to study changes related to disease processes and dietary modification.

Demountable liquid/flow cell for in vivo infrared microspectroscopy of biological specimens.

We have developed a liquid/flow cell/chamber allowing infrared measurements of living biological specimens with high spatial resolution under a controlled aqueous environment. This flow chamber features sub-micrometer thick diamond windows exhibiting low spherical and chromatic aberrations. Diamond has excellent transmission properties and minimal dispersion over the entire mid-infrared and visible spectral ranges. In contrast to current commercially available infrared liquid chambers, the flow chamber has a slim profile, which accommodates high resolution/magnification microscope objectives with small working distances, down to 0.6 mm above the chamber and 6 mm below the flow chamber. We have coupled a pump to the flow chamber to provide medium exchange. As an example, we present microspectroscopic infrared maps and spectra of the freshwater green alga Micrasterias sp. in the new flow chamber and compare them to maps obtained with a conventional liquid chamber. Pulse-amplitude-modulated fluorescence measurements on Micrasterias sp. cells inside the new flow chamber have been evaluated to demonstrate the viability of the algal cells.