Ablation of single-crystalline cesium iodide by extreme ultraviolet capillary-discharge laser

NUKLEONIKA 2020;65(4):205210 doi: 10.2478/nuka-2020-0031 ORIGINAL PAPER Introduction Laser ablation has been investigated for several decades. Laser ablation and desorption phenomena are of practical importance in numerous diverse applications. In the present study, we ablated a typical ionic crystal, i.e., cesium iodide (CsI), by short-wavelength nanosecond laser pulses. In the past, attempts have been made to ablate CsI to prepare thin fi lms by pulsed laser deposition (PLD) [1] with conventional, long-wavelength Ablation of single-crystalline cesium iodide by extreme ultraviolet capillary-discharge laser Jan Wild , Peter Pira , Tomas Burian , Ludek Vysin , Libor Juha , Zdenek Zelinger , Stanislav Danis , Vaclav Nehasil , Zdenek Rafaj , Vaclav Nevrly , Michal Dostal , Petr Bitala , Pavel Kudrna, Milan Tichy, Jorge J. Rocca J. Wild Faculty of Mathematics and Physics, Charles University V Holesovickach 2, 180 00 Praha 8, Czech Republic and Faculty of Safety Engineering, VSB – Technical University of Ostrava, Lumírova 630/13, 700 30 Ostrava, Czech Republic E-mail: [email protected] P. Pira, S. Danis, V. Nehasil, Z. Rafaj, P. Kudrna, M. Tichy Faculty of Mathematics and Physics, Charles University V Holesovickach 2, 180 00 Praha 8, Czech Republic T. Burian Faculty of Mathematics and Physics, Charles University V Holesovickach 2, 180 00 Praha 8, Czech Republic and Institute of Physics of the Czech Academy of Sciences, v.v.i., Na Slovance 2, 182 21 Praha 8, Czech Republic and J. Heyrovsky Institute of Physical Chemistry of the Czech Academy of Sciences, v. v. i., Dolejškova 2155/3, 182 23 Praha 8, Czech Republic V. Nevrly, P. Bitala Faculty of Safety Engineering, VSB – Technical University of Ostrava Lumírova 630/13, 700 30 Ostrava, Czech Republic L. Vysin Institute of Physics of the Czech Academy of Sciences v.v.i., Na Slovance 2, 182 21 Praha 8, Czech Republic L. Juha Institute of Physics of the Czech Academy of Sciences, v.v.i., Na Slovance 2, 182 21 Praha 8, Czech Republic and Institute of Plasma Physics of the Czech Academy of Sciences, v.v.i., Za Slovankou 3, 182 00 Praha 8, Czech Republic Abstract. Extreme ultraviolet (XUV) capillary-discharge lasers (CDLs) are a suitable source for the effi cient, clean ablation of ionic crystals, which are obviously diffi cult to ablate with conventional, long-wavelength lasers. In the present study, a single crystal of cesium iodide (CsI) was irradiated by multiple, focused 1.5-ns pulses of 46.9-nm radiation delivered from a compact XUV-CDL device operated at either 2-Hz or 3-Hz repetition rates. The ablation rates were determined from the depth of the craters produced by the accumulation of laser pulses. Langmuir probes were used to diagnose the plasma plume produced by the focused XUV-CDL beam. Both the electron density and electron temperature were suffi ciently high to confi rm that ablation was the key process in the observed CsI removal. Moreover, a CsI thin fi lm on MgO substrate was prepared by XUV pulsed laser deposition; a fraction of the fi lm was detected by X-ray photoelectron spectroscopy. Keywords: Ablation • CsI • Desorption • Laser • PLD • XUV Z. Zelinger J. Heyrovsky Institute of Physical Chemistry of the Czech Academy of Sciences, v. v. i., Dolejškova 2155/3, 182 23 Praha 8, Czech Republic M. Dostal Faculty of Safety Engineering, VSB – Technical University of Ostrava Lumírova 630/13, 700 30 Ostrava, Czech Republic and J. Heyrovsky Institute of Physical Chemistry of the Czech Academy of Sciences, v. v. i., Dolejškova 2155/3, 182 23 Praha 8, Czech Republic J. J. Rocca NSF ERC for Extreme Ultraviolet Science and Technology, Department of Electrical and Computer Engineering, Colorado State University Fort Collins, CO 805 23, USA Received: 14 November 2019 Accepted: 30 March 2020 © 2020 J. Wild et al. This is an open access article distributed under the Creative Commons AttributionNonCommercial-NoDerivatives 3.0 License (CC BY-NC-ND 3.0). 206 J. Wild et al. lasers [2, 3]. There are at least two strong sources of motivation for coating a chosen substrate with CsI. A thin fi lm of CsI serves as (a) a widely used photocathode [4]; and (b) a traditional scintillator material [5, 6]. Recently, the nonthermal ablation of CsI induced by femtosecond visible laser pulses was also reported [7]. The very weak linear absorption of visible radiation in CsI encourages the use of extreme ultraviolet (XUV) and soft X-ray lasers to ablate the ionic crystal effectively [8, 9]. The absorption of short-wavelength radiation occurs due to an atomic photoeffect. The absorption is strong because CsI is composed of heavy elements and has a relatively high density, i.e., 4.51 g/cm3. In this study, the source of short-wavelength radiation was a desktop capillary-discharge laser (CDL) providing nanosecond pulses of 46.9-nm radiation at a repetition rate up to 12 Hz [10]. The XUV-CDL- -induced ablation of the ionic crystal was studied both experimentally and by numerical modelling, and the etch rates and ablation thresholds were determined. The XUV-CDL-produced ablation plume was diagnosed by a Langmuir double probe [11, 12] to reveal the fundamental parameters of the plasma, i.e., its electron temperature and electron density. To test the possibility of using the plume for PLD purposes, the attempt to create a thin CsI layer on the MgO substrate was undertaken. Experimental The arrangement of the XUV laser–matter interaction experiment is shown in Fig. 1. The angle of incidence between the surface normal and the focused laser beam was 0°, i.e., irradiation was performed under normal incidence conditions. The parameters were the focus–target distance (z scan with Dz = 0.2 mm) and the number of pulses (10, 20, 30, 50, 100, and 111 pulses). The target was a single crystal of CsI placed on a motorized xyz positioning stage. The pressure in the vacuum interaction chamber was 10–5 mbar. The source of XUV radiation was a compact Ne-like collisionally pumped Ar CDL [10] with a 21-cm-long Al2O3 argon-fi lled capillary emitting at a wavelength of 46.9 nm (i.e., photon energy of 26.4 eV). XUV pulses provided by the CDL device exhibited a duration and energy of 1.5 ns (full width at half maximum (FWHM)) and up to 10 mJ, respectively. The CDL beam was focused using a 50-cm focal length Sc/Si multilayer mirror with a refl ectivity of 30% [13]. The CDL repetition rate was 2 Hz and 3 Hz for the ablation investigation and the PLD test, respectively. Pulse energy of 2 mJ was registered at the target surface after beam guiding and focusing in the vacuum interaction chamber. This value was considered during an estimation of the XUV laser fl uence. From the mathematical model of the beam caustics [13] and the known energy delivered within the pulse, the maximum power density on the sample surface was found to be as high as approximately 250 MW/cm2. After irradiation, the target surface was analysed by an optical surface profi ler based on white light interferometry (WLI; Zygo NewView 7300). The WLI data were analysed using Gwyddion software [14]. The optical profi ler provided information on the crater shapes and ablation depths. An analysis of the craters produced at various fl uences enabled determination of the ablation threshold. The experimentally determined value was compared to the value calculated using the XUV-ABLATOR computer code [15]. In a previous work [12], we measured both the electron temperature and the density of the plasma plume produced by the XUV-CDL beam focused on a bismuth (Bi) target with a Langmuir probe in both the single and double versions. In the present study, the double-probe technique was applied because the target was an insulator. The measurement was conducted using two parallel tungsten wires with lengths of 1 mm and diameters of 0.1 mm. The distance between the wires was 0.7 mm, and the plane of the wires was parallel to the surface of the target. The probe was located 0.6 mm from the target. To minimize the increased noise level of the electrically insulating target (CsI), we used batteries to bias the probe instead of the standard direct current (DC) power supply utilized in our previous work [12], in which the target was a good conductor (Bi). The target was held on a rotating stage. A CsI thin layer deposited on the MgO substrate by PLD using the experimental arrangement shown in Fig. 1 was characterized ex situ by means of X-ray photoelectron spectroscopy (XPS). The XPS measurements were performed in a ultra-high vacuum (UHV) chamber with a base pressure of about 5 × 10–10 mbar. The system was equipped with a Mg/Al dual-anode X-ray source, an Omicron EA 125 hemispherical electron analyzer with a total resolution of about 1 eV [16]. AlK radiation, with primary energy = 1486.6 eV, was used in this particular experiment. The binding energies (EB) of the obtained photoelectron spectra were calibrated using C1s line at EB = 284.5 eV. Results and discussion The typical shape of a crater produced in the single- -crystalline CsI by the focused XUV-CDL beam is shown in Fig. 2. Multiple pulse irradiations were performed using different numbers of shots, and the resulting series of craters was analysed. As shown in Fig. 3, the maximum depth of a particular crater increases with the number of pulses. The width of a crater is almost independent of the number of laser pulses. For a few pulses, the ablation rate (i.e., the thickness of the material layer removed by one pulse, Fig. 4) decreases, reaching a plateau at 100 pulses. This decrease was previously found for other ionic crystals [15]. This effect could be caused by (a) radiation- -induced hardening of the irradiated material and/ or (b) the development of the crater shape, which obstructs the exit of the material from the crater, enhancing its redeposition on the crater wall. 207Ablation of single-crystalline cesium iodide by extreme ultraviolet capillary-discharge laser Ablation threshold evaluation Ablation is a threshold process. For the estimation of a fl uence threshold Fth (i.e., the maximum fl uence when the etch rate is equal to zero), we use the Beer–Lambert law: (1) d = a ln(F/Fth) where d is the maximum crater depth, a is the attenuation length of the 46.9-nm radiation in CsI (38 nm as calculated using Henke’s tables [17]), and F is the focused laser beam fl uence. In Fig. 5, the data are shown after being processed using Eq. (1). Fth is computed from constant c in the linear fi t, as follows: (2) y = x + c Fig. 1. Experimental arrangement. (a) The plasma plume is measured by a pair of probes; (b) for the deposition of the thin fi lm, an MgO (001) substrate was placed in the probe position at a distance of 2 mm from the target. Not to scale. Fig. 2. (a) WLI image of the CsI surface after XUV-CDL-induced ablation at a fl uence value slightly above the ablation threshold. The image was taken by a Zygo optical profi ler after 100 laser pulses. (b) The maximum depth of the crater is 3.5 mm. The ablation processes dominate the material removal. WLI = white light interferometry. Fig. 3. Dependence of the maximum crater depth on the number of laser pulses. Fig. 4. Dependence of the etch rate on the number of pulses. Fig. 5. Dependence of the etch rate on the fl uence. Etch rates were calculated from the 30-shot z scan (‘a’ is the attenuation length). 208 J. Wild et al. (the red line in Fig. 5), where y is d/a, x is the estimation of ln(F) as ln((Ey)/S), and c is equal to –ln(Fth). Further, S is the experimentally measured area of the focused beam on the irradiated surface from the 30-shot ablation patterns. For a similar number of pulses, the maximum etch rate in CsI (60 nm) is approximately three times higher than the value obtained previously in LiF (20 nm [18]). The difference can be explained by the attenuation lengths of 46.9-nm radiation in CsI and LiF, which are 38 nm and 13.6 nm, respectively. The threshold fl uence for the XUV-CDL-induced ablation of CsI is Fth = 105 mJ/cm2 (the data used for this estimation are shown in Fig. 5). This estimation is the upper level of the ablation threshold for a single-shot process because of the declining etch rate. Numerical modelling of the XUV-induced CsI removal, performed with the 1D fi nite-difference Lagrangian code (XUV-ABLATOR [15]), provides a prediction of the maximum CsI etch rate, d 62 ± 11 nm per pulse, at a peak fl uence of 0.375 J/cm2 achieved in a tight focus. Computer simulations revealing the etch rate dependence on the fl uence (Fig. 6) indicate that the ablation threshold is approximately 0.15 J/cm2. This value is in good agreement with the threshold obtained experimentally. The ablation threshold obtained here in CsI is very close to the values of 0.06 J/cm2 [18] and 0.1 J/cm2 [19] found previously for LiF, which is an expected result because in CsI and LiF, the attenuation length of the 46.9-nm radiation is 38 nm and 13.6 nm, respectively, and the lattice energy is 5.7 eV and 10.56 eV, respectively [20]. In contrast to LiF, the longer attenuation length in CsI (38 nm) results in a lower energy density in the near-surface region at the same surface fl uence; however, a lower amount of energy is required to decompose the CsI lattice (5.7 eV). Therefore, the XUV-CDL energy densities needed to trigger the ablation of CsI and LiF are similar. The ablation threshold at 0.1 J/cm2 found for 1.5-ns pulses of XUV laser radiation is located lower than the ablation threshold 0.25 J/cm2 determined in CsI illuminated by 50-fs pulses of visible radiation (400 nm; second harmonic of Ti:sapphire laser) [7]). Even taking into account an order of magnitude difference in attenuation length (which could be revealed from the etch rates), the XUV laser ablation begins at much lower irradiances (approximately 70 MW/cm2) than the ablation induced by ultrashort pulses of visible laser radiation, which requires at least 5000 GW/cm2. The difference in thresholds can be explained by a difference in the photon energies. Even a single photon of XUV laser radiation carries enough energy to induce a point defect in the CsI lattice, while in the visible spectral range, multiphoton absorption is needed to reach energies able to damage the lattice. The probability of multiphoton processes is signifi cantly lower with respect to single-photon effects. Therefore, the threshold irradiance should be much higher when long-wavelength laser radiation is utilized to ablate an ionic crystal. The determination of the ablation threshold at ~0.1 J/cm2 sheds light on a previous soft X-ray laser experiment conducted with CsI [6]. In that experiment, radioluminescence of CsI was induced by a Ne-like quasi-steady-state collisionally pumped Zn soft X-ray laser (wavelength: 21.2 nm, pulse duration: 80 ps). Experiments were conducted with irradiance of 1.0 GW/cm2 or 6.7 MW/cm2 at the sample surface. The highest intensity was obtained by adding a Si/Mo multilayer mirror to the laser to form a half-cavity that allows for double-pass amplifi cation [6]. The arrangement with the half- -cavity corresponds to lower yield (lower effi ciency of the soft X-ray-laser-induced luminescence) in comparison to the lower irradiance case without the half-cavity. Our results indicate that substantial decomposition of the lattice could be responsible for the lack of luminescence effi ciency at higher irradiance (i.e., during the irradiation by the laser with the half-cavity) reported earlier [6]. Plasma characterization A typical signal obtained from the double probe immersed in the plasma plume is shown in Fig. 7. Registered data were processed by techniques described in detail elsewhere [12]. The plasma parameters in the plume are as follows: the electron temperature Te reaches 7.5 eV and the electron density ne is 8.7 × 1014 m–3. Both values are signifi cantly higher than the parameters of the Bi plasma achieved in our previous study [12]. The difference in density may be due to the ablation characteristic of CsI removal, in contrast to the desorption phenomena (as defi ned, e.g., in an earlier paper [21]) responsible for the formation of the Bi plasma plume reported previously [12]. A desorption process, even if induced by energetic photons, typically removes a thin layer of material per laser pulse [22]. Ablation blows off much more material than desorption. The dense material ablated by the front of the incoming XUV-CDL pulse is effi ciently ionized and heated by the remainder of the pulse, which results in higher electron density ne. The higher Fig. 6. Etch rates calculated by the XUV-ABLATOR code at increasing XUV-CDL fl uences. The results predicted with the initial setup of the input parameters (dotted line with star symbol) are depicted together with the values of the etch rate of the sample (box and whiskers) obtained by a quasi-Monte Carlo approach considering the relevant uncertainties of the modelling input parameters. 209Ablation of single-crystalline cesium iodide by extreme ultraviolet capillary-discharge laser electron temperature registered in the present study is also due to the difference in thermophysical properties of the chosen targets: in the case of CsI, ablation takes place and the ablation plasma plume formed under the given conditions contains a higher amount of energy. This is so mostly due to the fact that CsI is an insulator, in which the rapid release of the energy absorbed by heat conduction from the near-surface region into the bulk of the target is not possible, in contrast to the case of a conductor, such as Bi. Thin fi lm preparation For the purpose of thin fi lm preparation, 10 000 laser pulses (corresponding to the lifetime of one capillary) were used. X-ray photoelectron spectroscopy (XPS) spectra have demonstrated that deposition by the PLD method is partially successful. Using the ratio of the substrate signal (Mg 1s peak – not presented here) and the intensity of the deposited Cs 3d doublet, it can be concluded that the deposited amount of CsI is equivalent only to a fraction of the monolayer. The Cs 3d doublet spectrum is presented in Fig. 8. The binding energies EB = 725.8 eV and 739.8 eV correspond to Cs 3d3/2 and 3d5/2 peaks, respectively. Cs is probably in the iodide or oxide form. The EB of 3d5/2 electrons in these species should be about 724 eV. The higher EB measured corresponds to the supposed thin noncontinuous deposited fi lm. No signal of iodide was indicated in the spectra. It is possible that in the early phase of thin layer formation, the crystal CsI was not created, so that iodide atoms tend to sublimate. Note that a thin layer prepared by another capillary laser CAPEX [23] showed similar properties. Conclusions Taking into account the uncertainty related to the absolute calibration of the pulse energy measurement and the shot-to-shot fl uctuations of the XUV-CDL output energy, it can be concluded that the experimentally determined etch rates and the threshold fl uence for CsI are reproducible and can be compared to the values obtained in computer simulations conducted with the XUV-ABLATOR code. The agreement between the experiment and theory is satisfactory – the ablation threshold is located at ~0.1 J/cm2 in both cases. The erosion of irradiated material is mainly due to ablation, with the desorption process playing a minor role. Ablation dominates the erosion processes because the XUV-CDL-induced rate of material removal quickly exceeds the attenuation length of the XUV laser radiation in the material. This fact is also supported by results of the double-probe measurement. The electron temperature of the plasma plume (~7.5 eV) is noticeably higher than in the case of Bi plasma [12]. The low effectiveness of material transfer during PLD is a result of the relatively low pulse energy delivered by the XUV-CDL device at the 2-Hz repetition rate used in this experiment. The pulse energy of the XUV-CDL is at the microjoule level, whereas standard UV excimer lasers, which are typically used in PLD experiments, deliver hundreds of millijoules in a single pulse. Nevertheless, this study has produced one of the fi rst thin fi lms of an ionic crystal material, which has been prepared by PLD with an XUV laser and, at the same time, it has showed the possibility of further investigation in the early phases of thin fi lm growth. Acknowledgments. This work was supported by the VSB–Technical University of Ostrava Project no. SP2020/162. The Colorado State University researchers also acknowledge the support of an award from the National Science Foundation [PHY-1004295]. ORCID P. Bitala http://orcid.org/0000-0001-5953-9295 T. Burian http://orcid.org/0000-0003-3982-9978 S. Danis http://orcid.org/0000-0001-5884-882X M. Dostal http://orcid.org/0000-0002-8129-7410 L. Juha http://orcid.org/0000-0003-4189-8753 V. Nehasil http://orcid.org/0000-0003-3057-5780 V. Nevrly http://orcid.org/0000-0003-4606-3966 P. Pira http://orcid.org/0000-0002-8829-7958 Z. Rafaj http://orcid.org/0000-0001-5962-5388 J. J. Rocca http://orcid.org/0000-0002-8349-6907 L. Vysin http://orcid.org/0000-0002-8549-0859 J. Wild http://orcid.org/0000-0003-2216-2898 Z. Zelinger http://orcid.org/0000-0002-7342-3640 Fig. 7. Double-probe signals registered in the plasma plume normal to the CsI target surface (the target-probe distance is 0.6 mm). Fig. 8. XPS signal of the submonolayer deposited on the MgO substrate showing Cs peaks of 3d3/2 and 3d5/2. 210 J. Wild et al. References 1. Chrisey, D., & Hubler, G. (1994). Pulsed laser deposition of thin fi lms. New York: Wiley. 2. Fernández-Lima, F., Collado, V., Ponciano, C., Farenzena, L., Pedrero, E., & da Silveira, E. (2003). Laser ablation of CsI analyzed by delayed extraction. Appl. Surf. Sci., 217(1/4), 202–209. DOI: 10.1016/ s0169-4332(03)00547-6. 3. Brendel’, V. M., Bukin, V. V., Garnov, S. V., Bagdasarov, V. Kh., Denisov, N. N., Garanin, S. G., Terekhin, V. A., & Trutnev, Y. A. (2012). Fabrication of alkali halide UV photocathodes by pulsed laser deposition. Quantum Electron., 42(12), 1128–1132. DOI: 10.1070/qe2012v042n12abeh014916. 4. Breskin, A. (1996). CsI UV photocathodes: history and mystery. Nucl. Instrum. Methods Phys. Res. Section A-Accel. Spectrom. Detect. Assoc. Equ., 371(1/2), 116–136. DOI: 10.1016/0168-9002(95)01145-5. 5. Nikl, M. (2006). Scintillation detectors for x-rays. Meas. Sci. Technol., 17(4), R37–R54. DOI: 10.1088/09570233/17/4/r01. 6. Jaeglé, P., Sebban, S., Carillon, A., Jamelot, G., Klisnick, A., Zeitoun, P., Rus, B., Nantel, M., Albert, F., & Ros, D. (1997). Ultraviolet luminescence of CsI and CsCl excited by soft x-ray laser. J. Appl. Phys., 81(5), 2406–2409. DOI: 10.1063/1.364246. 7. Hada, M., Zhang, D., Pichugin, K., Hirscht, J., Kochman, M., Hayes, S. A., Manz, S., Gengler, R. Y. N., Wann, D. A., Seki, T., Moriena, G., Morrison, C. A., Matsuo, J., Sciaini, G., & Miller, R. J. D. (2014). Cold ablation driven by localized forces in alkali halides. Nature Commun., 5(1), 3863–3870. DOI: 10.1038/ ncomms4863. 8. Juha, L., Bittner, M., Chvostova, D., Krasa, J., Kozlov, M., Pfeifer, M., Polan, J., Pr ä g, A. R., Rus, B., Stupka, M., Feldhaus, J., Letal, V., Otcenasek, Z., Krzywinski, J., Nietubye, R., Pelka, J. B., Andrejczuk, A., Sobierajski, R., Ryc, L., Boody, F. P., Fiedorowicz, H., Bartnik, A. S., Mikolajczyk, J., Rakowski, R., Kubat, P., Pina, L., Horvath, M., Grisham, M. E., Vaschenko, G. O., Menoni, C. S., & Rocca, J. J. (2005). Short-wavelength ablation of molecular solids: pulse duration and wavelength effects. J. Microlithogr. Microfabr. Microsyst., 4(3), 033007. DOI: 10.1117/1.2037467. 9. Juha, L., Bittner, M., Chvostova, D., Krasa, J., Otcenasek, Z., Präg, A., Ullschmied, J., Pientka, Z., Krzywinski, J., Pelka, J. B., Wawro, A., Grisham, M. E., Vaschenko, G., Menoni, C. S., & Rocca, J. J. (2005). Ablation of organic polymers by 46.9-nm-laser radiation. Appl. Phys. Lett., 86(3), 034109. DOI: 10.1063/1.1854741. 10. Heinbuch, S., Grisham, M., Martz, D., & Rocca, J. (2005). Demonstration of a desk-top size high repetition rate soft x-ray laser. Opt. Express, 13(11), 4050–4055. DOI: 10.1364/opex.13.004050. 11. Chung, P., Talbor, L., & Touryan, K. (1975). Electric probes in stationary and fl owing plasmas. BerlinHeidelberg-New York: Springer-Verlag. 12. Pira, P., Burian, T., Kolpaková, A., Tichý, M., Kudrna, P., Daniš, S., Juha, L., Lancok, J., Vysin, L., Civis, S., Zelinger, Z., Kubat, P., & Wild, J. (2014). Langmuir probe measurement of the bismuth plasma plume formed by an extreme-ultraviolet pulsed laser. J. Phys. D-Appl. Phys., 47(40), 405205. DOI: 10.1088/00223727/47/40/405205. 13. Vysin, L., Burian, T., Chalupsky, J., Grisham, M., Hajkova, V., Heinbuch, S., Jakubczak, K., Martz, D., Mocek, T., Pira, P., Polan, J., Rocca, J. J., Rus, B., Sobota, J., & Juha, L. (2009). Characterization of focused beam of desktop 10-Hz capillary-discharge 46.9-nm laser. Proc. SPIE, 7361, 73610O. 14. Nečas, D., & Klapetek, P. (2012). Gwyddion: An open-source software for SPM data analysis. Centr. Eur. J. Phys., 10(1), 181–188. DOI: 10.2478/s11534011-0096-2. 15. Blejchař, T., Nevrlý, V., Vašinek, M., Dostál, M., Kozubková, M., Dlabka, J., Stachon, M., Juha, L., Bitala, P., Zelinger, Z., Pira, P., & Wild, J. (2016). Desorption/ ablation of lithium fl uoride induced by extreme ultraviolet laser radiation. Nukleonika, 61(2), 131–138. DOI: 10.1515/nuka-2016-0023. 16. Ševčíková, K., Nehasil, V., Vorokhta, M., Haviar, S., Matolín, V., Matolínová, I., Masek, K., Pis, I., Kobayashi, K., Kobata, M., Nagata, T., Matsushita, Y., & Yoshikawa, H. (2015). Altering properties of cerium oxide thin fi lms by Rh doping. Mater. Res. Bull., 67, 5–13. DOI: 10.1016/j.materresbull.2015.02.059. 17. Henke, B. L., Gullikson, E. M., & Davis, J. C. (1993). X-ray interactions: photoabsorption, scattering, transmission, and refl ection at E=50-30,000 eV, Z = 1-92. Atom. Data Nucl. Data Tables, 54(2), 181–342. 18. Pira, P., Burian, T., Vysin, L., Chalupsky, J., Lancok, J., Wild, J., Strizik, M., Zelinger, Z., Rocca, J. J., & Juha, L. (2011). Ablation of ionic crystals induced by capillarydischarge XUV laser. Proc. SPIE, 8077, 807719. 19. Ritucci, A., Tomassetti, G., Reale, A., Arrizza, L., Zuppella, P., Reale, L., Palladino, L., Flora, F., Bonfi gli, F., Faenov, A., Pikuz, T., Kaiser, J., Nilsen, J., & Jankowski, A. F. (2006). Damage and ablation of large bandgap dielectrics induced by a 46.9 nm laser beam. Optics Lett., 31(1), 68–70. DOI: 10.1364/ol.31.000068. 20. Budylin, B., & Vorobev, A. (1964). Effect of radiation on ionic structures. Jerusalem: Israel Program for Scientifi c Translations. 21. Haglund, R. (1996). Microscopic and mesoscopic aspects of laser-induced desorption and ablation. Appl. Surf. Sci., 96/98, 1–13. DOI: 10.1016/01694332(95)00371-1. 22. Chalupský, J., Juha, L., Hájková, V., Cihelka, J., Vyšín, L., Gautier, J., Hajdu, J., Hau-Riege, S. P., Jurek, M., Krzywinski, J., London, R. A., Papalazarou, E., Pelka, J. B., Rey, G., Sebban, S., Sobierajski, R., Stojanovic, N., Tiedtke, K., Toleikis, S., Tschentscher, T., Valentin, C., Wabnitz, H., & Zeitoun, P. (2008). Non-thermal desorption/ablation of molecular solids induced by ultra-short soft x-ray pulses. Opt. Express, 17(1), 208–217. DOI: 10.1364/oe.17.000208. 23. Frolov, O., Kolacek, K., Schmidt, J., Straus, J., Choukourov, A., & Pira, P. (2016). Ablation of LiF and CsI by EUV nanosecond laser pulse. In International Conference on X-ray Lasers (pp. 327–331). Cham, Switzerland: Springer.