@misc{juha_radiation_damage_2009, 
author={Juha, L.,Hajkova, V.,Chalupsky, J.,Vorlicek, V.,Ritucci, A.,Reale, A.,Zuppella, P.,Stoermer, M.},
title={Radiation damage to amorphous carbon thin films irradiated by multiple 46.9 nm laser shots below the single-shot damage threshold},
year={2009},
howpublished = {journal article},
doi = {https://doi.org/10.1063/1.3117515},
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 extreme ultraviolet laser (CDL=capillary-discharge laser; XUV=extreme ultraviolet, i.e., wavelengths below 100 nm). The laser wavelength and pulse duration were 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%. The laser pulse energy was varied from 0.4 to 40  µJ on the sample surface. The irradiation was carried out at five fluence levels between 0.1 and 10  J/cm2, accumulating five different series of shots, i.e., 1, 5, 10, 20, and 40. The damage to the a-C thin layer was investigated by atomic force microscopy (AFM) and Nomarski differential interference contrast (DIC) optical microscopy. The dependence of the 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  µm using AFM data, assuming the beam to have a Gaussian profile. Such a plot can also be used for a determination of single-shot damage threshold in a-C. A single-shot threshold value of 1.1  J/cm2 was found. Investigating the 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 thin a-C layers, 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 microprobe analysis 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 earlier [L. Juha et al., Proc. SPIE 5917, 91 (2005)] on an a-C sample irradiated by a large number of femtosecond pulses of XUV high-order harmonics.},
note = {Online available at: \url{https://doi.org/10.1063/1.3117515} (DOI). Juha, L.; Hajkova, V.; Chalupsky, J.; Vorlicek, V.; Ritucci, A.; Reale, A.; Zuppella, P.; Stoermer, M.: Radiation damage to amorphous carbon thin films irradiated by multiple 46.9 nm laser shots below the single-shot damage threshold. Journal of Applied Physics. 2009. vol. 105, no. 9, 093117. DOI: 10.1063/1.3117515}}