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Proceedings Paper

X-ray optics for study of ultrafast processes in crystalline samples
Author(s): Eckhart Foerster; Ingo Uschmann; O. Wehrhan; Andreas Morak; Thomas Feurer; Roland A. Sauerbrey; D. Boschetto; Antoine Rousse; Daniele Hulin
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Paper Abstract

Non-thermal melting of semiconductor crystals, phase transitions on a sub-picosecond time scale can be studied by optical pump x-ray probe experiments. Powerful femtosecond lasers deliver brilliant ultrashort K(alpha ) pulses on a time scale from 100 fs to 1 ps that can be optimized for these pump-probe experiments. These experiments consist of two diffracting elements: (i) a bent crystal imaging the flash x-ray source in a narrow spectral window; and (ii) the sample crystal diffracting the ultrashort x-ray pulse. As penetration depths of optical pump beam are usually much shorter than x-ray extinction depths, best sensitivity to ultrafast structural changes is obtained for minimum x-ray extinction depths. This can be achieved by selecting samples containing heavy elements, thin crystalline film samples and by using asymmetric Bragg reflections, respectively. Several theoretical codes have been developed to optimize design of the instruments. X-ray topographic cameras and diffractometers were modified for fabrication and characterization of 2D bent crystals. Best practical results were obtained when structurally perfect wafers of Si, Ge, and quartz crystals were prepared while monitored by x-ray topography and diffractometry. After a final check of x-ray imaging and reflection properties of the toroidal crystals, monochromatic x-ray beam and laser pump beam are adjusted spatially to coincide on the sample crystal. Because converging x-rays impinge on the sample crystal, its rocking curve can be registered as a spatial distribution on the detector. In comparison to synchrotron experiments where about 104 pulses must be integrated, in these experiments rocking curves can be recorded in a single or in a few laser shots. Ultrafast processes are studied in Langmuir Blodgett films containing Cd, in bulk semiconductors, such as InSb, and in CdTe semiconductor films. Focused, pulsed monochromatic x-rays have been transmitted through biological samples to register many reflections, which opens the way to ultrafast studies in structural biology.

Paper Details

Date Published: 14 November 2001
PDF: 6 pages
Proc. SPIE 4504, Applications of X Rays Generated from Lasers and Other Bright Sources II, (14 November 2001); doi: 10.1117/12.448461
Show Author Affiliations
Eckhart Foerster, Friedrich-Schiller-Univ. Jena (Germany)
Ingo Uschmann, Friedrich-Schiller-Univ. Jena (Germany)
O. Wehrhan, Friedrich-Schiller-Univ. Jena (Germany)
Andreas Morak, Friedrich-Schiller-Univ. Jena (Germany)
Thomas Feurer, Friedrich-Schiller-Univ. Jena (Germany)
Roland A. Sauerbrey, Friedrich-Schiller-Univ. Jena (Germany)
D. Boschetto, Ecole Nationale Superieure des Techniques Avancees (Germany)
Antoine Rousse, Ecole Nationale Superieure des Techniques Avancees (France)
Daniele Hulin, Ecole Nationale Superieure des Techniques Avancees (France)

Published in SPIE Proceedings Vol. 4504:
Applications of X Rays Generated from Lasers and Other Bright Sources II
George A. Kyrala; Jean-Claude J. Gauthier, Editor(s)

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