Proceedings Article | 18 May 2009
J. Cihelka, L. Juha, J. Chalupský, F. Rosmej, O. Renner, K. Saksl, V. Hájková, L. Vyšin, E. Galtier, R. Schott, A. Khorsand, D. Riley, T. Dzelzainis, A. Nelson, R. Lee, P. Heimann, B. Nagler, S. Vinko, J. Wark, T. Whitcher, S. Toleikis, T. Tschentscher, R. Faustlin, H. Wabnitz, S. Bajt, H. Chapman, J. Krzywinski, R. Sobierajski, D. Klinger, M. Jurek, J. Pelka, S. Hau-Riege, R. London, J. Kuba, N. Stojanovic, K. Sokolowski-Tinten, A. Gleeson, M. Störmer, J. Andreasson, J. Hajdu, N. Timneanu
Proc. SPIE. 7361, Damage to VUV, EUV, and X-Ray Optics II
KEYWORDS: Mirrors, Chemical species, Spectroscopy, Copper, Ions, Silicon, Emission spectroscopy, Aluminum, Free electron lasers, Plasma
The beam of Free-Electron Laser in Hamburg (FLASH) tuned at either 32.5 nm or 13.7 nm was focused by a grazing
incidence elliptical mirror and an off-axis parabolic mirror coated by Si/Mo multilayer on 20-micron and 1-micron spot,
respectively. The grazing incidence and normal incidence focusing of ~10-fs pulses carrying an energy of 10 μJ lead at
the surface of various solids (Si, Al, Ti, Ta, Si3N4, BN, a-C/Si, Ni/Si, Cr/Si, Rh/Si, Ce:YAG, poly(methyl methacrylate)
- PMMA, stainless steel, etc.) to an irradiance of 1013 W/cm2 and 1016 W/cm2, respectively. The optical emission of the
plasmas produced under these conditions was registered by grating (1200 lines/mm and/or 150 lines/mm) spectrometer
MS257 (Oriel) equipped with iCCD head (iStar 720, Andor). Surprisingly, only lines belonging to the neutral atoms
were observed at intensities around 1013 W/cm2. No lines of atomic ions have been identified in UV-vis spectra emitted
from the plasmas formed by the FLASH beam focused in a 20-micron spot. At intensities around 1016 W/cm2, the OE
spectra are again dominated by the atomic lines. However, a weak emission of Al+ and Al2+ was registered as well. The
abundance ratio of Al/Al+ should be at least 100. The plasma is really cold, an excitation temperature equivalent to 0.8 eV was found by a computer simulation of the aluminum plasma OE spectrum. A broadband emission was also
registered, both from the plasmas (typical is for carbon; there were no spectral lines) and the scintillators (on Ce:YAG
crystal, both the luminescence bands and the line plasma emission were recorded by the spectrometer).
