Ultrafast structural changes in the subpicosecond time domain were studied by using X-rays produced by a femtosecond laser. An upgraded 1 kHz table-top laser was used for optical pump X-ray probe experiments on germanium crystals. The number of laser generated Ti Kα and Cu Kα photons are either 5×10¹⁰ or 1.2×10¹⁰ per second. In this study, the Ti Kα rays were Bragg reflected on the 311 net planes of a toroidal silicon crystal. The germanium sample crystal was placed in the focus of the Ti Kα radiation and reflected it from the 111 plane to be detected by a CCD camera. An ultrafast optical pulse caused by the same kHz laser generates reversible strain pulses in the germanium crystal. By using different time delays between pump and probe pulses time-resolved rocking curves were obtained. The thermoelastic model of Thomsen, used in rocking curve simulations satisfactorily, explains the main features of strain evolution in Ge. Explanation of the remaining deviations between experimental and simulated curves needs a consideration of band gap deformation potential to be included in the simulation.

Date Published: 11 October 2005
PDF: 11 pages
Proc. SPIE 5958, Lasers and Applications, 59581Z (11 October 2005); doi: 10.1117/12.641082

Published in SPIE Proceedings Vol. 5958:
Lasers and Applications
Krzysztof M. Abramski; Antonio Lapucci; Edward F. Plinski, Editor(s)