Open Access
Add to BibSonomy
Abstract
In this paper, improved operation of a high-contrast, high-brightness ultraviolet laser system is described. The laser system is based on a conventional short-pulse dye/excimer design, modified to contain 3 KrF excimer short-pulse amplifiers and the recently developed nonlinear Fourier-filtering stage for contrast improvement. The final amplifier accepts a beam size of ~4x4 cm2, producing 100 mJ energy of short-pulses using a two-beam interferometric multiplexing setup. Temporal measurements of the output showed positively chirped pulses of ~700 fs duration, beside a focusability of ~2 times the diffraction limit. Amplified spontaneous emission—as the only source of the temporal background—results in a focused intensity contrast of >1012 in the entire temporal window. These unique parameters give access to laser-matter interaction experiments above 1019 W/cm2 intensity at 248 nm.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
The remarkable progress in the generation of intense electromagnetic fields is driven by the chirped pulse amplification (CPA) technique using solid state (Ti:sapphire) lasers. The peak power of these laser systems surpasses the PW level and the focused intensities are up to the 1022-1023 W/cm2 range [1–6]. However, in case of laser-matter interaction experiments one of the key challenge is to produce temporally and spatially clean, high-contrast pulses [7–9]. Pre-pulses and ASE of 107-108 W/cm2 intensity can change laser-matter interactions considerably [10,11], which sets the necessary temporal contrast beyond 1014. Therefore several techniques have been introduced to improve the temporal contrast of high intensity laser systems. The most straightforward methods are the plasma mirror technique [12,13] or frequency conversion [14,15] at the end of the laser system or the use of XPW technique in a Double-CPA arrangement [6,16–18]. With the use of these techniques the temporal contrast reaches 1010 and 1012 on the ns scale. However, the imperfect compensation of the spectral phase during compression and/or re-scattering on the compressor elements yields a coherent pedestal (from 105 to 1010) on the ps scale, which seems an inherent shortcoming of the CPA technique [2,4–6,8,16–18].
Better focusability (~1/λ2) and higher photon energy (~1/λ) are the main figures of merit of high-intensity, ultraviolet short-pulses. Short-pulse ultraviolet (UV) laser systems are therefore efficient tools to produce high-intensity fields even for moderate power level. High-brightness, UV short-pulse laser systems are therefore complementary sources for a wide range of laser-matter experiments such as generation of XUV/X-ray radiation, sub-micron machining [19] or experiments where plasma instabilities are more pronounced [20].
There are several ways to produce high-intensity pulses in the UV part of the spectrum. One possible way is to apply frequency conversion of radiation from a TW-class IR laser. This approach is however extremely difficult considering the energy (~100 mJ) and pulse duration (sub-ps) desired for laser-matter experiments and this method has not been successfully developed. The most straightforward way is to use dual-wavelength systems. In these systems the generation and amplification of the short pulse is done at two different wavelengths including frequency doubling [21,22] or tripling [23] before the UV amplifiers. Using the so called active spatial filtering method [24] for frequency conversion the temporal and spatial quality of the UV seed pulse is very high before amplification.
KrF excimer is a high gain medium and best suited for short pulse amplification in the UV [25]. The KrF medium has low saturation energy density (2 mJ/cm2) and narrow spectral bandwidth (∆λ/λ≈1/300) compared to solid state lasers, therefore much larger beam/amplifier cross-sections are needed for the same output power, thus limiting the presently achievable peak power to the TW range [25]. The optimum energy density range for short pulse amplification (~1.1 εsat – 2.2εsat) in terms of energy extraction and contrast is determined by the simultaneous effects of saturated amplification and non-saturated absorption. In order to maintain the optimum operational conditions during amplification amplifiers of increasing electrode separation are applied combining with off-axis amplification [26] and a slightly divergent beam.
KrF excimer is a four-level gain medium where the pumping has to be fast compared to the relaxation time of the upper pumped level (~10ns) and of the excited lasing level (~ns). For this reason, the amplification time window primarily is not determined by the storage time of the medium, but by the duration of the pumping which is ~15ns in our case. In case of multi-pass amplification the pump laser and the amplifiers have to be synchronized to each other with ~ns accuracy. Another consequence of the short storage time - compared to the pumping - is that the short pulse has only access to a fraction of the whole optical energy - called as momentarily stored energy. The only way to increase the accessible energy is to subsequently repeat the amplification steps. In order the keep the energy density in the optimum range, the use of multiplexing is necessary. Interferometric multiplexing introduced in [27] ensures automatic phase-control of the partial beams.
KrF excimer amplifiers have the benefit that the low saturation energy density allows direct amplification of short pulses, therefore the only source of the temporal background is the ASE. This is one of the main advantage of short-pulse excimer systems compared to solid-state laser systems. The shorter wavelength also allows smaller focal spot and the low density gaseous media ensures smaller phase-front distortions during amplification.
KrF short-pulse excimer lasers using a Ti:Sa based front end in general can produce short UV pulses at higher repetition rate (up to 300 Hz), therefore higher average power. In [23] and [28] 30 mJ energy with 270 fs pulse duration and 50 mJ with 600 fs pulse duration was achieved. By the use of a dye-excimer hybrid system where the seed pulse was generated by a sub-ps dye laser system and the amplification in the UV was carried out by two KrF excimer amplifiers 100 mJ output energy was achieved [28]. The final amplification stage used an interferometric multiplexing setup in a two-beam, double-pass arrangement. The best arrangement in terms of peak energy and peak power was presented in [29,30] where a Ti:Sa front end produced the seed pulses and 300-500 mJ pulse energy, 200-300 fs pulse duration and with f/2 focusing ~2 μm focal spot was achieved. These short-pulse KrF excimer laser systems can produce >1019 W/cm2 focused intensity (or >1021 W/cm2sterad−1 brightness) despite their moderate power level [23,31].
The lack of CPA scheme results a uniform distribution temporal background even in the ps vicinity of the main pulse. However, due to the short wavelength the ASE has a rapidly growing feature and sets the temporal contrast to ~1010 already for ~10 mJ output energy at 248 nm. In case of additional amplification pulse cleaning is needed between the amplifiers to maintain and/or to improve the above contrast.
Plasma mirror technique was successfully applied for KrF laser systems, where ~70% reflectivity and 102-103 contrast improvement was demonstrated [32]. Recently, an alternative method called nonlinear Fourier-filtering (NFF) was introduced to filtering short UV pulses [33,34]. A contrast improvement of >105 and an internal efficiency is above 40% was demonstrated. This method is also applicable for solid state based laser systems. In this arrangement an annular beam is focused into a gas jet where the self-generated plasma introduces nonlinear phase-modulation of the different diffraction orders of the beam (see second half of Fig. 1). On the other hand the low intensity ASE is not (or negligibly) modulated, where the same annular beam is imaged at the output. However, the main pulse - which undergoes π phase shift in an ideal case - has a significantly modified output distribution and becomes spatially separable from the temporal background. It was shown that the achievable contrast improvement is primarily limited by the spatial contrast of imaging [34], which can be improved significantly by adjusting the spatial frequency spectrum of the annular beam to the capabilities of the imaging system. For this reason a low NA pre-imaging (practically a spatial filter) is implemented before the nonlinear Fourier filter as shown in the first half of Fig. 1.
In this paper the implementation of the nonlinear Fourier-filter into a high-brightness KrF excimer laser system is reported. This system contains three excimer gain modules of increasing cross section allowing an output beam size of ~4x4 cm2. The amplifiers are used in a double-pass off-axis arrangement and the final amplifier is complemented by a two-beam interferometric multiplexing scheme. The nonlinear Fourier-filter is placed after the first pre-amplifier providing sub-mJ, high-contrast seed pulses for the following amplifiers. After the temporal filtering the energy of the pulse is boosted up to 100 mJ. Focusability measurements showed that the beam is ~2 times diffraction limited and has a smooth, flat-topped near-field distribution. The lack of the CPA scheme results in uniform temporal distribution of the background, on the other hand the output pulse remains positively chirped. The energy of ASE has a rapidly growing feature, therefore its intensity strongly depends on the value of the overall applied gain. The unique parameters of the output pulses give access to >1019 W/cm2 focused intensity of above 1011 temporal contrast at 248 nm.
2. Experimental setup
Figure 2 shows the schematic of the high-contrast, high-brightness UV laser system based on the above described principles. The seed pulse is generated in a femtosecond dye laser system pumped by a commercially available XeCl excimer laser [25]. The seed pulse generation is based on a distributed feedback dye laser providing pulses of several times 100 fs at 497 nm. (Alternatively such as in [23] a solid state based front end is also applicable for seed pulse generation.) In our case the pulses are frequency doubled using a BBO crystal placed in the Fourier-plane of the beam (active spatial filtering) [24]. The nonlinear conversion results in not only temporal but effective spatial filtering as well. As a consequence, high-contrast, nearly Gaussian UV pulses of ~15-20 μJ energy are available before the first KrF pre-amplifier.
Fig. 2 Schematic of the high-contrast, high-brightness KrF laser system. (SHG:second harmonic generation, PI: low numerical aperture pre-imaging, BS: beam splitter, for details see text.)
Based on the former experiments a certain limit of intensity (~1014 W/cm2) has to be reached to produce the nonlinear phase-shift in the Fourier-filter. For stable operation of the filter - besides the desired intensity level - the most important requirement is the regular far-field distribution of the annular beam. The internal efficiency of the technique is above 40%, however losses caused by the UV optics (windows and lenses) are considerable. Therefore the nonlinear Fourier-filter has been implemented after the first pre-amplifier, where the intensity limit can be reached easily with stable spatial distribution and the following amplifiers can compensate for the energy loss caused by the filter and by the associated UV optics.
The low numerical aperture pre-imaging (PI on Fig. 2) is a simple way to create an annular beam of reduced spatial frequency components and to achieve >5 order of magnitude contrast improvement as it was theoretically and experimentally verified in [34]. Therefore an annular beam block was placed after the first pass and imaged trough a vacuum pinhole to exclude the higher spatial frequencies and the spatially incoherent background. The image of the beam-block complemented by a second annular beam-block acts as an input for the nonlinear Fourier-filter. In this way the theoretically achievable highest contrast improvement is reached.
After the temporal filtering the second KrF pre-amplifier is used in a double pass arrangement to boost up the energy to the level desired by the final amplification stage. The final amplification stage having an effective cross section of ~4x4 cm2 is used in a double-pass two beam multiplexing arrangement. This setup gives access to higher portion of the energy stored in the amplifier.
The two pre-amplifiers are driven by a common pumping circuit providing automatic synchronization. The pumping circuits of the XeCl pump laser, the pre-amplifiers and the final amplifier are synchronized by an in-house designed active synchronization unit, which can compensate for the long-time drift.
3. Experimental results
Discharge pumped KrF excimer amplifiers have larger shot-to-shot fluctuations compared to solid-state lasers. Stable operation of the nonlinear filter is crucial to the operation of the following amplifiers, thus for the output pulse parameters. Deep saturation of amplification can compensate fluctuations introduced by former elements of the laser system but this condition adversely affects the contrast. Figure 3(a) shows the typical far field distribution of the annular beam before the NFF. For comparison the far field distribution of an ideal annular beam is shown in Fig. 3(b). Our experiments showed that the beam contains high spatial frequency fluctuations and inhomogeneity. As a consequence of the inhomogeneity the far field distribution of the annular beam does not have circular symmetry, which is certainly caused by the difference of the vertical and horizontal distribution of the discharge of KrF preamplifiers. The effect of misalignments and inhomogeneity of the beam in principle can also influence the stability of the filter. This important topic - due to its complexity - will be discussed in details in an upcoming paper.
The nonlinear Fourier-filtering has a similar arrangement as in [33,34]. In this case we use ~f/60 focusing to reach few times 1015 W/cm2 intensity in the focal plane. As a result of the stable performance of the nonlinear filter ~0.5 mJ energy pulses of very high contrast are available for further amplification. To minimize the contrast degradation for further amplification the energy density of the pulse is kept close to the saturation level of the amplifiers, by the use of the greatest off-axis angle allowed by the geometry of amplifiers (~2.8 degrees). The energy of the pulse after the second pre-amplifier is about 15 mJ resulting in an energy contrast of ~50 referred to the ASE. The spatial distribution of the beam is circular (diameter 2.5 cm) and nearly flat-topped. Figure 4 shows the far field distribution of the beam with f/150 focusing. For comparison the far field distribution of an ideal diffraction limited beam is also shown (black curves). The beam is ~1.5 times diffraction limited, contrarily the ASE has a much (> 3∙105 times) larger solid angle. The temporal measurements of the short pulse and the ASE showed a ratio of 3∙104 of temporal duration, together with the above parameters the intensity contrast is > 4.5x1011.
Fig. 4 Far field distribution of the amplified beam after the second KrF pre-amplifier. The cross-section along the x and y axis are shown by the red curves. For comparison an ideal diffraction limited beam is also shown by the black curves.
It is important to note that the ASE after the second amplifier is measured to be generated mainly by this amplifier (after the temporal filtering). In fact by blocking the beam after the temporal filter no change in the energy, spatial or temporal distribution of the ASE could be detected.
The near field distribution of the output beam after the final amplifier is shown in Fig. 5, which shows the already diffracted (Fresnel number of 300) output beam. However, it can be seen that the beam has a nearly flat-topped profile.
The far field distribution of the output beam is shown in Fig. 6. For comparison it also shows the far field distribution of an ideal diffraction limited flat-topped beam. It can be seen that the beam is ~2 times diffraction limited using f/30 focusing.
Fig. 6 Far field distribution of the amplified beam after the final amplifier. The cross-section along the x and y axis are shown by the red curves. For comparison an ideal diffraction limited beam is also shown by the black curves.
The ASE after the final amplifier still has a ~3∙105 times larger solid angle compared to the main pulse. Worth to note that the ASE generated before the temporal filter is not detectable in terms of energy, temporal or spatial distribution at the output of the laser system indicating that it has no contribution to the final contrast. The spectrum of the input beam (after the frequency conversion) and output are shown in Figs. 7(a) and 7(b). The output spectrum is slightly modified compared to the input spectrum.
The second-order autocorrelation curve of the output main pulse is shown in Fig. 8. To measure the output pulse duration a second-order autocorrelator was used. The autocorrelator - described in [21] - is based on a Michaelson-interferometer, where an ionization gas cell filled with NO serves as the detector. NO shows no single photon, but pronounced two-photon absorption at 248 nm, therefore the measured ion signal is the second order function of the intensity. The output pulse duration is ~700 fs with remarkable positive chirp caused by the lenses and the windows of amplifiers and vacuum tubes of the system.
The final amplifier stage uses an interferometric multiplexing setup in a two-beam, double-pass arrangement. In this way the energy of the short pulse is boosted up to 100 mJ (4% of rms stability) and the energy contrast ratio is >10. The regular spatio-temporal distribution of the ASE - supported by careful measurements - ensures that the intensity contrast in the far field can be determined by multiplying the energy, the pulse duration and the solid angle ratio between the main pulse and the ASE. This calculation gives us a value 9x1010 for intensity contrast.
It is worth to mention, that the energy of the ASE is highly dependent on the applied gain while the amplification of the short pulse shows saturation. Lowering the applied gain after the temporal filter (by introducing attenuation before the final amplifier stage) results in an output energy of 50 mJ and an energy contrast of >100. This means that for 50 mJ output energy the intensity contrast in the far field reaches the 9x1011 value. In principle the above described laser system provides >1019 W/cm2 intensity.
4. Conclusions
In conclusion we demonstrate the operation of nonlinear Fourier-filter integrated into a high-brightness KrF ultraviolet laser system. Using an amplifier chain consisting of 3 KrF short-pulse amplifiers and a nonlinear Fourier filter integrated after the first pre-amplifier we produced short pulses of 100 mJ energy, ~700 fs pulse duration (positively chirped) ~2 times limited by diffraction and 1011 focused intensity contrast. This laser system with its unique parameters gives access to laser-matter interaction experiments at 1019 W/cm2 intensity level with high contrast at 248 nm.
Funding
Hungarian Scientific Research Fund (OTKA113222); European Union's Horizon 2020 research and innovation program (654148); Laserlab-Europe co-financed by the European Social Fund (EFOP-3.6.2-16-2017-00005- Ultrafast physical processes in atoms, molecules, nanostructures and biological systems); Ministry of Human Capacities (UNKP-17-1 New National Excellence Program and the Hungary grant 20391-3/2018/FEKUSTRAT).
References
1. V. Yanovsky, V. Chvykov, G. Kalinchenko, P. Rousseau, T. Planchon, T. Matsuoka, A. Maksimchuk, J. Nees, G. Cheriaux, G. Mourou, and K. Krushelnick, “Ultra-high intensity- 300-TW laser at 0.1 Hz repetition rate,” Opt. Express 16(3), 2109–2114 (2008). [CrossRef] [PubMed]
2. Z. Wang, C. Liu, Z. Shen, Q. Zhang, H. Teng, and Z. Wei, “High-contrast 1.16 PW Ti:sapphire laser system combined with a doubled chirped-pulse amplification scheme and a femtosecond optical-parametric amplifier,” Opt. Lett. 36(16), 3194–3196 (2011). [CrossRef] [PubMed]
3. M. Martinez, W. Bang, G. Dyer, X. Wang, E. Gaul, T. Borger, M. Ringuette, M. Spinks, H. Quevedo, A. Bernstein, M. Donovan, and T. Ditmire, “The Texas petawatt laser and current experiments,” AIP Conf. Proc. 1507, 874–878 (2012).
4. F. Wagner, C. P. João, J. Fils, T. Gottschall, J. Hein, J. Körner, J. Limpert, M. Roth, T. Stöhlker, and V. Bagnoud, “Temporal contrast control at the PHELIX petawatt laser facility by means of tunable sub-picosecond optical parametric amplification,” Appl. Phys. B 116(2), 429–435 (2014). [CrossRef]
5. T. M. Jeong and J. Lee, “Femtosecond petawatt laser,” Ann. Phys. 526(3–4), 157–172 (2014). [CrossRef]
6. Y. Chu, X. Liang, L. Yu, Y. Xu, L. Xu, L. Ma, X. Lu, Y. Liu, Y. Leng, R. Li, and Z. Xu, “High-contrast 2.0 Petawatt Ti:sapphire laser system,” Opt. Express 21(24), 29231–29239 (2013). [CrossRef] [PubMed]
7. T. Ceccotti, A. Lévy, H. Popescu, F. Réau, P. D’Oliveira, P. Monot, J. P. Geindre, E. Lefebvre, and P. Martin, “Proton acceleration with high-intensity ultrahigh-contrast laser pulses,” Phys. Rev. Lett. 99(18), 185002 (2007). [CrossRef] [PubMed]
8. A. Flacco, F. Sylla, M. Veltcheva, M. Carrié, R. Nuter, E. Lefebvre, D. Batani, and V. Malka, “Dependence on pulse duration and foil thickness in high-contrast-laser proton acceleration,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 81, 036405 (2010). [CrossRef] [PubMed]
9. J. S. Green, A. P. L. Robinson, N. Booth, D. C. Carroll, R. J. Dance, R. J. Gray, D. A. MacLellan, P. McKenna, C. D. Murphy, D. Rusby, and L. Wilson, “High efficiency proton beam generation through target thickness control in femtosecond laser-plasma interactions,” Appl. Phys. Lett. 104(21), 214101 (2014). [CrossRef]
10. K. B. Wharton, C. D. Boley, A. M. Komashko, A. M. Rubenchik, J. Zweiback, J. Crane, G. Hays, T. E. Cowan, and T. Ditmire, “Effects of nonionizing prepulses in high-intensity laser-solid interactions,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 64, 025401 (2001). [CrossRef] [PubMed]
11. I. B. Földes, J. S. Bakos, K. Gál, Z. Juhász, M. A. Kedves, G. Kocsis, S. Szatmári, and G. Veres, “Properties of high harmonics generated by ultrashort UV laser pulses on solid surfaces,” Laser Phys. 10(1), 264–269 (2000).
12. H. C. Kapteyn, M. M. Murnane, A. Szoke, and R. W. Falcone, “Prepulse energy suppression for high-energy ultrashort pulses using self-induced plasma shuttering,” Opt. Lett. 16(7), 490–492 (1991). [CrossRef] [PubMed]
13. C. Thaury, F. Quéré, J.-P. Geindre, A. Levy, T. Ceccotti, P. Monot, M. Bougeard, F. Réau, P. D’Oliveira, P. Audebert, R. Marjoribanks, and P. H. Martin, “Plasma mirrors for ultrahigh-intensity optics,” Nat. Phys. 3(6), 424–429 (2007). [CrossRef]
14. A. Marcinkevičius, R. Tommasini, G. D. Tsakiris, K. J. Witte, E. Gaižauskas, and U. Teubner, “Frequency doubling of multi-terawatt femtosecond pulses,” Appl. Phys. B 79(5), 547–554 (2004). [CrossRef]
15. D. Hillier, C. Danson, S. Duffield, D. Egan, S. Elsmere, M. Girling, E. Harvey, N. Hopps, M. Norman, S. Parker, P. Treadwell, D. Winter, and T. Bett, “Ultrahigh contrast from a frequency-doubled chirped-pulse-amplification beamline,” Appl. Opt. 52(18), 4258–4263 (2013). [CrossRef] [PubMed]
16. A. Ricci, A. Jullien, J.-P. Rousseau, Y. Liu, A. Houard, P. Ramirez, D. Papadopoulos, A. Pellegrina, P. Georges, F. Druon, N. Forget, and R. Lopez-Martens, “Energy-scalable temporal cleaning device for femtosecond laser pulses based on cross-polarized wave generation,” Rev. Sci. Instrum. 84(4), 043106 (2013). [CrossRef] [PubMed]
17. Y. Xu, Y. Leng, X. Guo, X. Zou, Y. Li, X. Lu, C. Wang, Y. Liu, X. Liang, R. Li, and Z. Xu, “Pulse temporal quality improvement in a petawatt Ti:Sapphire laser based on cross-polarized wave generation,” Opt. Commun. 313, 175–179 (2014). [CrossRef]
18. M. P. Kalashnikov, E. Risse, H. Schönnagel, and W. Sandner, “Double chirped-pulse-amplification laser: a way to clean pulses temporally,” Opt. Lett. 30(8), 923–925 (2005). [CrossRef] [PubMed]
19. P. Simon, J. Bekesi, C. Dölle, J.-H. Klein-Wiele, G. Marowsky, S. Szatmari, and B. Wellegehausen, “Ultraviolet femtosecond pulses: key technology for sub-micron machining and efficient XUV pulse generation,” Appl. Phys. B 74(S1), s189–s192 (2002). [CrossRef]
20. W. L. Kruer, “The physics of laser plasma interactions,” Westview Press, (2003).
21. S. Szatmári and F. P. Schäfer, “Simplified laser system for the generation of 60 fs pulses at 248 nm,” Opt. Commun. 68(3), 196–202 (1988). [CrossRef]
22. S. V. Alekseev, A. I. Aristov, Ya. V. Grudtsyn, N. G. Ivanov, B. M. Koval’chuk, V. F. Losev, S. B. Mamaev, G. A. Mesyats, L. D. Mikheev, Yu. N. Panchenko, A. V. Polivin, S. G. Stepanov, N. A. Ratakhin, V. I. Yalovoi, and A. G. Yastremskii, “Visible-range hybrid femtosecond systems based on a XeF(C–A) amplifier: state of the art and prospects,” Quantum Electron. 43(3), 190–200 (2013). [CrossRef]
23. J. Békési, S. Szatmári, P. Simon, and G. Marowsky, “Table-top KrF amplifier delivering 270 fs output pulses with over 9 W average power at 300 Hz,” Appl. Phys. B 75(4), 521–524 (2002).
24. S. Szatmári, Z. Bakonyi, and P. Simon, “Active spatial filtering of laser beams,” Opt. Commun. 134(1–6), 199–204 (1997). [CrossRef]
25. S. Szatmári, G. Marowsky and P. Simon, “Femtosecond excimer lasers and their applications,” Landolt–Börnstein New Series (Springer, 2007), pp. 215–253.
26. G. Almàsi, S. Szatmári, and P. Simon, “Optimized operation of short-pulse KrF amplifiers by off-axis amplification,” Opt. Commun. 88(2-3), 231–239 (1992). [CrossRef]
27. S. Szatmári and P. Simon, “Interferometric multiplexing scheme for excimer amplifiers,” Opt. Commun. 98(1-3), 181–192 (1993). [CrossRef]
28. J. Békési, G. Marowsky, S. Szatmári, and P. Simon, “A 100 mJ table-top short pulse amplifier for 248 nm using interferometric multiplexing,” Z. Phys. Chem. 215(12), 1543 (2001). [CrossRef]
29. A. B. Borisov, J. C. McCorkindale, S. Poopalasingam, J. W. Longworth, P. Simon, S. Szatmári, and C. K. Rhodes, “Rewriting the rules governing high intensity interactions of light with matter,” Rep. Prog. Phys. 79(4), 046401 (2016). [CrossRef] [PubMed]
30. F. G. Omenetto, K. Boyer, J. W. Longworth, A. McPherson, T. Nelson, P. Noel, W. A. Schroeder, C. K. Rhodes, S. Szatmári, and G. Marowsky, “High-brightness terawatt KrF* (248 nm) system,” Appl. Phys. B 64(6), 643–646 (1997). [CrossRef]
31. S. Szatmári, G. Almási, M. Feuerhake, and P. Simon, “Production of intensities of 10^19 W/cm^2 by a table-top KrF laser,” Appl. Phys. B 63(5), 463–466 (1996). [CrossRef]
32. B. Gilicze, A. Barna, Z. Kovács, S. Szatmári, and I. B. Földes, “Plasma mirrors for short pulse KrF lasers,” Rev. Sci. Instrum. 87(8), 083101 (2016). [CrossRef] [PubMed]
33. S. Szatmári, R. Dajka, A. Barna, B. Gilicze, and I. B. Földes, “Improvement of the temporal and spatial contrast for high-brightness laser beams,” Laser Phys. Lett. 13(7), 075301 (2016). [CrossRef]
34. B. Gilicze, R. Dajka, I. B. Földes, and S. Szatmári, “Improvement of the temporal and spatial contrast of the nonlinear Fourier-filter,” Opt. Express 25(17), 20791–20797 (2017). [CrossRef] [PubMed]
