High – performance LiF crystal and film quantum beam detectors for high-resolution imaging

Date	Do, 12.12.2013 - Do, 12.12.2013
Time	10.15
Speaker	Prof. Anatoly Faenov, Joint institute for High Temperature, Russian Academy of Sciences, Moscow, Russia and, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Japan
Location	Universität Bern, Institut für Angewandte Physik, Gebäude exakte Wissenschaften, Hörsaal B116, Sidlerstrasse 5, 3012 Bern
Program	Main principles of operation and review of results, obtained by using recently proposed high-performance imaging detector, based on formation of color centers in LiF crystal and film will be presented. It will be discussed applications of such detectors for: 1) Submicron soft X-ray radiography of low-contrast objects, including nanofoils, membranes and biological structures. A spatial resolution of ~ 700 nm in the field of view of few square centimeters has been demonstrated in the imaging system consisted of a specially developed, very bright, debris-free femtosecond-laser-driven cluster-based plasma soft X-ray source and a submicron, high dynamic range LiF crystal detector. High performance absorption and propagation-based phase-contrast images of ultrathin foils with few nanometer variations of thickness and of micron size point defects presence have been obtained. The homogeneity of 100 nm Mo or Zr foils were measured with the accuracy ± 3%. Altogether, it has opened a new opportunity for novel ultrafast soft X-ray diagnostics and metrology of large size free standing or mesh supported nano-thickness foils or other nanostructures. 2) In situ sub-micron measurements of near-field and far-field properties of soft X-ray laser-driven transient-collision plasma and free electron laser beams. It has been shown that due to favorable combination of high spatial resolution, high dynamic range and wide field of view the LiF detectors allow measuring a highly detailed intensity distribution across the full size of the beams well as permit to evaluate spatial distribution of coherence and spectral properties of radiation across the beam. Newly applied, based on the diffraction imaging of periodical structures illuminated by investigated beam allowed to estimated accuracy of measurements in order of ~ 10-20%. 3) A single shot imaging of relativistic high order harmonic (HOH) beams. That is a new type of HOH, generated by an oscillating electron spikes formed in underdense gas jet plasma created by relativistically self-focusing laser pulses. The LiF film was used for near-field diffraction imaging of the HOH beam and investigation of its coherent properties. The focusability of the HOH beam was investigated using spherical Mo/Si mirror and LiF crystal. Using such technique the sizes and complexity of the HOH source structure have been measured with spatial resolution of ~ 200 nm. 4) High-performance neutron imaging. It was demonstrated that the LiF detectors have practically linear response on the thermal neutron fluence in the dynamic range of at least 103 and allow obtaining neutron radiographic images with spatial resolution of ~ 5 μm. The images are almost free from granular noise. Moreover, detailed evaluation using a standard sensitivity indicator for neutron radiography showed that two holes with less than 2% transmittance differences could be distinguished. Additionally, we recently demonstrated that the high resolution neutron imaging with LiF crystals could be useful for quantitative characterizations of neutron sources and electric devices, comprising of low-Z elements, for example, such as fuel cells. All of this gives new opportunity for microns scale spatial resolution imaging by neutrons in areas, where a high spatial resolution with a high image gradation resolution is needed.
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