Jiri Limpouch

Enhancement of laser/EUV conversion by shaped laser pulse interacting with Li-contained targets for EUV lithography

The advantages of droplet and claster Li-contained targets for debris free EUV generation are estimated on base of analytical modeling and simulation. Conversion efficiency of laser energy into EUV energy from such targets is found to reach a few percents. The laser prepulse is proposed to enhance the laser energy conversion into emission at wavelength of 13.5 nm.

Metal-like self-organization of periodic nanostructures on silicon and silicon carbide under femtosecond laser pulses

Periodic structures were generated on Si and SiC surfaces by irradiation with femtosecond laser pulses. Self-organized structures with spatial periodicity of approximately 600u2009nm appear on silicon and silicon carbide in the laser fluence range just above the ablation threshold and upon irradiation with a large number of pulses. As in the case of metals, the dependence of the spatial periodicity on laser fluence can be explained by the parametric decay of laser light into surface plasma waves. The results show that the proposed model might be universally applicable to any solid state material.

Spectroscopic characterization of plasma densities of laser-irradiated Al foils

Detailed spectroscopic analysis of K-shell emission simultaneously observed at the irradiated and unirradiated surface of laser-exploded foils is reported. The space-dependent spectral line widths and relative shifts in the positions of the Al Lyman transition are interpreted in terms of the plasma density variations; the trend in the shifts data supports the idea of a density-dependent line shift. The significant features of the spectra emitted from the densest part of the plasma are compared with predictions from standard diagnostics modeling based on codes MEDUSA and FLY, and with the results of 2D ATLANT hydrodynamic simulations post-processed with a novel suite of atomic physics codes XEPAP. The results obtained corroborate the feasibility of the plasma density diagnostics based on line shifts in the intermediately coupled plasmas.

Optimal lithium targets for laser-plasma lithography

Lithium containing droplet and cluster targets irradiated by laser pulses are proposed as prospective source of for soft x-ray lithography. Analytical model and simulations show that laser with repetition rate of several MHz with energy of several mJ and pulse duration 10 ps is required.

Soft X-ray emission from molybdenum plasmas generated by dual laser pulses

We demonstrate efficient enhancement of soft X-ray (SXR) emission from molybdenum plasmas produced using dual pulse irradiation, in which 10-ns and 150-ps pre-pulses were followed by a 150-ps main pulse. The number of photons was observed to be 5.3u2009×u20091016 photons/sr, which corresponded to a conversion efficiency of 1.5%/sr in λu2009=u20092.34–4.38u2009nm region at a pulse separation time of 1u2009ns with the 150-ps pre-pulse. The conversion efficiency became 1.3 times as large as that produced by a single pulse. The results indicate the advantage of dual pulse irradiation using sub-ns pre-and main pulses to produce the bright plasmas required for applications such as laboratory based SXR microscopy.

XUV spectra of 2nd transition row elements: identification of 3d–4p and 3d–4f transition arrays

The use of laser produced plasmas (LPPs) in extreme ultraviolet/soft x-ray lithography and metrology at 13.5 nm has been widely reported and recent research efforts have focused on developing next generation sources for lithography, surface morphology, patterning and microscopy at shorter wavelengths. In this paper, the spectra emitted from LPPs of the 2nd transition row elements from yttrium (Z = 39) to palladium (Z = 46), with the exception of zirconium (Z = 40) and technetium (Z = 43), produced by two Nd:YAG lasers which delivered up to 600 mJ in 7 ns and 230 mJ in 170 ps, respectively, are reported. Intense emission was observed in the 2–8 nm spectral region resulting from unresolved transition arrays (UTAs) due to 3d–4p, 3d–4f and 3p–3d transitions. These transitions in a number of ion stages of yttrium, niobium, ruthenium and rhodium were identified by comparison with results from Cowan code calculations and previous studies. The theoretical data were parameterized using the UTA formalism and the mean wavelength and widths were calculated and compared with experimental results.

Laser ion acceleration: from present to intensities achievable at ELI-Beamlines

Simulation studies of laser-induced ion acceleration are extended from the present intensities up to ~1022 W/cm2 that will be achieved soon at the ELI-Beamlines facility in Prague. Numerical simulations of target normal sheath acceleration (TNSA) enhancement by micro-structures on the front and rear sides of thin foils will be extended to higher laser intensities together with a brief description of target preparation techniques. Computational study of the impact of laser polarization, laser incidence angle, foil thickness and material is presented for PW laser beam of intensity of the order 1022 W/cm2. Acceleration regime that combines TNSA with radiation pressure acceleration (RPA) is identified.

ELIMED: a new hadron therapy concept based on laser driven ion beams

Laser accelerated proton beams have been proposed to be used in different research fields. A great interest has risen for the potential replacement of conventional accelerating machines with laser-based accelerators, and in particular for the development of new concepts of more compact and cheaper hadrontherapy centers. In this context the ELIMED (ELI MEDical applications) research project has been launched by INFN-LNS and ASCR-FZU researchers within the pan-European ELI-Beamlines facility framework. The ELIMED project aims to demonstrate the potential clinical applicability of optically accelerated proton beams and to realize a laser-accelerated ion transport beamline for multi-disciplinary user applications. In this framework the eye melanoma, as for instance the uveal melanoma normally treated with 62 MeV proton beams produced by standard accelerators, will be considered as a model system to demonstrate the potential clinical use of laser-driven protons in hadrontherapy, especially because of the limited constraints in terms of proton energy and irradiation geometry for this particular tumour treatment. Several challenges, starting from laser-target interaction and beam transport development up to dosimetry and radiobiology, need to be overcome in order to reach the ELIMED final goals. A crucial role will be played by the final design and realization of a transport beamline capable to provide ion beams with proper characteristics in terms of energy spectrum and angular distribution which will allow performing dosimetric tests and biological cell irradiation. A first prototype of the transport beamline has been already designed and other transport elements are under construction in order to perform a first experimental test with the TARANIS laser system by the end of 2013. A wide international collaboration among specialists of different disciplines like Physics, Biology, Chemistry, Medicine and medical doctors coming from Europe, Japan, and the US is growing up around the ELIMED project with the aim to work on the conceptual design, technical and experimental realization of this core beamline of the ELI Beamlines facility.

Laser-produced post-pulse crater formation in solids observed in PALS facility interaction experiment

Results from PALS facility laser-massive Al target interaction experiments are reported. Main attention is devoted craters formation under the action of laser pulses of various energy (from 100 J up to 600 J), intensity (from 1013 W/cm2 up to 1015 W/cm2), laser wavelength (0.438 μm and 1.315 μm), and focal beam radius (from 35 μm up to 600 μm). Crater replicas were made of wax and their depths and radii were subsequently obtained by microscopy measurements. Duration of the laser-pulse-initiated shock wave propagation into the targets was much longer than that of the laser pulse itself (400 ps). This was an important feature of the experimental arrangement. Theoretical model of the post-pulse crater formation by the shock wave propagating and decaying in solids after the end of the laser pulse is presented and applied for explanation of the results obtained in experiments.

Conversion of ultrashort laser pulses into x-ray emission in high-density laser plasma

Various regimes of interaction of ultrashort laser pulses with solid targets in vacuum are analyzed. Analytical formulas that characterize plasma parameters and x-ray emission during the laser pulse are obtained in a very broad range of experimental parameters. For constant laser energy, the conversion efficiency into x rays during laser pulse is shown to grow with laser pulse length in all interaction regimes.