18 May 2009 Response of molecular solids to ultra-intense femtosecond soft x-ray pulses
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Abstract
Ultra-fast soft x-ray lasers have opened a new area of laser-matter interactions which in most cases differ from the well understood interaction of UV-vis radiation with solid targets. The photon energy >30eV essentially exceeds the width of band gap in any known material and excites the electrons from the deep atomic and valence levels directly to the conduction band. Both thermal and non-thermal phenomena can occur in such a material being caused by electron thermalization and bond breaking, respectively. We report the first observation of non-thermal single-shot soft x-ray laser induced desorption occurring below the ablation threshold in a thin layer of poly (methyl methacrylate) - PMMA. Irradiated by the focused beam from the Free-electron LASer in Hamburg (FLASH) at 21.7nm, the samples have been investigated by an atomic-force microscope (AFM) enabling the visualization of mild surface modifications caused by the desorption. A model describing non-thermal desorption and ablation has been developed and used to analyze singleshot imprints in PMMA. An intermediate regime of materials removal has been found, confirming the model predictions. We also report below-threshold multiple-shot desorption of PMMA induced by high-order harmonics (HOH) at 32nm as a proof of an efficient material removal in the desorption regime.
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J. Chalupský, L. Juha, V. Hájková, J. Cihelka, L. Vysin, J. Gautier, J. Hajdu, S. P. Hau-Riege, M. Jurek, J. Krzywinski, Ri. A. London, E. Papalazarou, J. B. Pelka, G. Rey, S. Sebban, R. Sobierajski, N. Stojanovic, K. Tiedtke, S. Toleikis, T. Tschentscher, C. Valentin, H. Wabnitz, P. Zeitoun, "Response of molecular solids to ultra-intense femtosecond soft x-ray pulses", Proc. SPIE 7361, Damage to VUV, EUV, and X-Ray Optics II, 736108 (18 May 2009); doi: 10.1117/12.822297; https://doi.org/10.1117/12.822297
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