New method for the determination of photoabsorption from transmittance measurements in the extreme ultraviolet.

We have developed a new method for the determination of photoabsorption at extreme ultraviolet wavelengths longer than 20 nm, where reliable refractive index values are sparse or non-existent. Our method overcomes the obstacle of multiple reflections that occur inside thin films in this spectral range, which up until now has prevented the accurate determination of photoabsorption from transmittance measurements. We have derived a mathematical expression that is independent of internal reflection amplitudes, while taking advantage of the transmittance oscillations stemming from such reflections.

Design of multilayer-based diagnostics for measurement of high energy x rays and gamma rays.

We investigate several possible multilayer-based optic designs for future hard x-ray and gamma ray diagnostics, including the detection and measurement of the positron annihilation radiation at 511 keV. The focus is set on increasing the photon efficiency and signal-to-noise ratio, compared to a previous multilayer-based system that was successfully employed to measure spectra in the 55 keV-100 keV range. Several possible designs using multilayer coatings are discussed, including mirror-based optics and multilayer Laue lenses.

Ultrafast multi-cycle terahertz measurements of the electrical conductivity in strongly excited solids.

Key insights in materials at extreme temperatures and pressures can be gained by accurate measurements that determine the electrical conductivity. Free-electron laser pulses can ionize and excite matter out of equilibrium on femtosecond time scales, modifying the electronic and ionic structures and enhancing electronic scattering properties. The transient evolution of the conductivity manifests the energy coupling from high temperature electrons to low temperature ions.

Depth-graded Mo/Si multilayer coatings for hard x-rays.

This manuscript presents the first systematic study of non-periodic, broadband Mo/Si multilayer coatings with and without B C interface barrier layers for hard x-ray applications with large field of view. The photon energy of operation in this work is 17.4 keV, the Mo Kα emission line.

Lifetime Stability and Microstructure Properties of Cr/B₄C X-ray Reflective Multilayer Coatings.

This paper demonstrates that highly reflective Cr/B₄C multilayer interference coatings with nanometric layer thicknesses, designed to operate in the soft X-ray photon energy range, have stable reflective performance for a period of 3 years after deposition. The microstructure and chemical composition of layers and interfaces within Cr/B₄C multilayers is also examined, with emphasis on the B₄C-on-Cr interface where a significant diffusion layer is formed and on the oxide in the top B₄C layer. Multiple characterization techniques (X-ray reflectivity at different photon energies, X-ray photoelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction) are employed and the results reveal a consistent picture of the Cr/B₄C layer structure.