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Proceedings Paper

Capillary-discharge 46.9-nm laser-induced damage to a-C thin films exposed to multiple laser shots below single-shot damage threshold
Author(s): L. Juha; V. Hájková; J. Chalupsky; V. Vorliček; A. Ritucci; A. Reale; P. Zuppella; M. Störmer
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Paper Abstract

High-surface-quality amorphous carbon (a-C) optical coatings with a thickness of 45 nm, deposited by magnetron sputtering on a silicon substrate were irradiated by the focused beam of capillary-discharge Ne-like Ar XUV laser (CDL). Laser wavelength and pulse duration were of 46.9 nm and 1.7 ns, respectively. The laser beam was focused onto the sample surface by a spherical Sc/Si multilayer mirror with a total reflectivity of about 30%. Laser pulse energy was on the sample surface varied from 0.4 &mgr;J to 40 &mgr;J. The irradiation was carried out at five fluence levels between 0.1 J/cm2 and 10 J/cm2, accumulating five different series of shots, i.e., 1, 5, 10, 20, and 40. The damage to a-C thin layer was investigated by atomic force microscopy (AFM) and Nomarski differential interference contrast (DIC) optical microscopy. Obtaining the dependence of single-shot-damaged area on pulse energy makes it possible to determine a beam spot diameter in the focus. Its value was found to be equal to (23.3±3.0) &mgr;m using AFM data and considering the beam to have a gaussian profile. Calculations based on a more realistic assumption about the beam profile are in progress. Such a plot can also be used for a determination of single-shot damage threshold in a-C. Single-shot threshold value of 1.1 J/cm2 was found by plotting the damaged areas determined by means of AFM. Investigating consequences of the multiple-shot exposure it has been found that an accumulation of 10, 20 and 40 shots at a fluence of 0.5 J/cm2, i.e., below the single-shot damage threshold, causes irreversible changes of a-C thin layer which can be registered by both the AFM and the DIC microscopy. In the center of the damaged area, AFM shows a-C removal to a maximum depth of 0.3, 1.2 and 1.5 nm for 10-, 20- and 40-shot exposure, respectively. Raman micro-probe does not indicate any change in the structure of the remaining a-C material. The erosive behavior, reported here, contrasts with the material expansion observed on the a-C sample irradiated by a large number of femtosecond pulses of XUV high-order harmonics (HHs).

Paper Details

Date Published: 23 May 2007
PDF: 7 pages
Proc. SPIE 6586, Damage to VUV, EUV, and X-ray Optics, 65860D (23 May 2007); doi: 10.1117/12.724602
Show Author Affiliations
L. Juha, Institute of Physics (Czech Republic)
V. Hájková, Institute of Physics (Czech Republic)
J. Chalupsky, Institute of Physics (Czech Republic)
Czech Technical Univ. in Prague (Czech Republic)
V. Vorliček, Institute of Physics (Czech Republic)
A. Ritucci, Univ. of L'Aquila, Lab. Nazionale del Gran Sasso, INFN (Italy)
A. Reale, Univ. of L'Aquila, Lab. Nazionale del Gran Sasso, INFN (Italy)
P. Zuppella, Univ. of L'Aquila, Lab. Nazionale del Gran Sasso, INFN (Italy)
M. Störmer, GKSS Research Ctr. (Germany)

Published in SPIE Proceedings Vol. 6586:
Damage to VUV, EUV, and X-ray Optics
Libor Juha; Ryszard H. Sobierajski; Hubertus Wabnitz, Editor(s)

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