11 October 2005 Ultrafast structural changes in germanium triggered by femtosecond laser pulses
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Abstract
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.
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Eckhart Förster, Eckhart Förster, Andreas Morak, Andreas Morak, Tino Kämpfer, Tino Kämpfer, Ingo Uschmann, Ingo Uschmann, Ortrud Wehrhan, Ortrud Wehrhan, Flavio Zamponi, Flavio Zamponi, } "Ultrafast structural changes in germanium triggered by femtosecond laser pulses", Proc. SPIE 5958, Lasers and Applications, 59581Z (11 October 2005); doi: 10.1117/12.641082; https://doi.org/10.1117/12.641082
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