Jaroslav Cihelka

Soft x-ray free electron laser microfocus for exploring matter under extreme conditions

We have focused a beam (BL3) of FLASH (Free-electron LASer in Hamburg: lambda = 13.5 nm, pulse length 15 fs, pulse energy 10-40 microJ, 5 Hz) using a fine polished off-axis parabola having a focal length of 270 mm and coated with a Mo/Si multilayer with an initial reflectivity of 67% at 13.5 nm. The OAP was mounted and aligned with a picomotor controlled six-axis gimbal. Beam imprints on poly(methyl methacrylate) - PMMA were used to measure focus and the focused beam was used to create isochoric heating of various slab targets. Results show the focal spot has a diameter of < or =1 microm. Observations were correlated with simulations of best focus to provide further relevant information.

A new series of 3,5-diamino-1,2,4-triazolium(1+) inorganic salts and their potential in crystal engineering of novel NLO materials

Seven inorganic salts of 3,5-diamino-1,2,4-triazole (dat) with inorganic acids were prepared within our project focused on the crystal engineering of novel NLO materials and their X-ray structures were determined. Three triclinic compounds, dat(1+) selenate dihydrate, dat(1+) sulphate dihydrate and dat(1+) perchlorate, crystallize in the space group P. Three monoclinic structures of dat(1+) – i.e. nitrate, chloride hemihydrate and hydrogen phosphite crystallize in P21/c, P21/n and P21/c, respectively. Finally, the most promising structure of dat(1+) dihydrogen phosphate is orthorhombic (the space group Fdd2). The structure is formed by anionic layers parallel to the ac plane and the cationic chains parallel to the c axis. The FTIR and Raman spectra of the title compounds have been recorded and discussed. The assignment of the spectra is based on a quantum-chemical calculation and the factor group analysis. Quantitative powder measurements of the second harmonic generation of the only non-centrosymmetric dat(1+) dihydrogen phosphate at 1064 nm were performed and a relative efficiency equal to KDP (i.e. potassium dihydrogen phosphate) was observed. The consequent study of single crystal samples enabled the estimation of NLO tensor coefficients of this material.

Spectroscopic Investigations of High-Power Laser-Induced Dielectric Breakdown in Gas Mixtures Containing Carbon Monoxide

Large-scale plasma was created in gas mixtures containing carbon monoxide by high-power laser-induced dielectric breakdown (LIDB). The composition of the mixtures used corresponded to a cometary and/or meteoritic impact into the Earths early atmosphere. A multiple-centimeter-sized fireball was created by focusing a single 85 J, 450 ps near-infrared laser pulse into the center of a 15 L gas cell. The excited reaction intermediates that formed in various stages of the LIDB plasma chemical evolution were investigated by optical emission spectroscopy (OES) with temporal resolution. Special attention was paid to any OES signs of molecular ions. However, carbon monoxide cations were registered only if their production was enhanced by Penning ionization, i.e., excess He was added to the CO. The chemical consequences of laser-produced plasma generation in a CO-N 2-H 2O mixture were investigated using high resolution Fourier-transform infrared absorption spectroscopy (FTIR) and gas chromatography (GC). Several simple inorganic and organic compounds were identified in the reaction mixture exposed to ten laser sparks. H 2 (18)O was used to avoid possible contamination. The large laser spark triggered more complex reactivity originating in carbon monoxide than expected, when taking into account the strong triple bond of carbon monoxide causing typically inefficient dissociation of this molecule in electrical discharges.

Semi-organic salts of aniline with inorganic acids: prospective materials for the second harmonic generation

Three novel inorganic salts of aniline with sulfuric and selenic acids were prepared and characterized by X-ray structural analysis. Anilinium(1+) selenate, (C6H5NH3+)2SeO42−, and anilinium sulfate, (C6H5NH3+)2SO42−, crystallize in the monoclinic space groupC2. The crystal structures are based on hydrogen bonded layers of alternating anilinium cations and inorganic anions. Anilinium(1+) selenate dihydrate, (C6H5NH3+)2SeO42−·2H2O, crystallizes in the monoclinic space groupC2/c. The crystal structure is formed by a network of alternating anilinium cations, selenate anions and water molecules connected by a system of intermolecular hydrogen bonds. The FTIR and Raman spectra of all the compounds have been recorded and discussed as well as their crystal structures. According to the DSC curves and temperature dependence of lattice parameters, anilinium sulfate exhibits phase transitions at 217 and 182 K. The appropriate changes of vibrational spectra were also recorded during cooling of the sample especially in the N–H stretching and sulfate antisymmetric stretching (ν3SO42−) spectral regions. The quantitative measurements of the second harmonic generation at 1064 nm were performed using powdered samples of anilinium sulfate, anilinium chloride and anilinium selenate, and the relative efficiencies deff = 0.05dKDP, deff = 2.33dKDP and deff = 0.05dKDP (KDP; i.e.KH2PO4) have been observed, respectively.

A High-Power Laser-Driven Source of Sub-nanosecond Soft X-Ray Pulses for Single-Shot Radiobiology Experiments

Abstract Davídková, M., Juha, L., Bittner, M., Koptyaev, S., Krása, J., Pfeifer, M., Štísová, V., Bartnik, A., Fiedorowicz, H., Mikolajczyk, J., Ryc, L., Pína, L., Horváth, M., Babánková, D., Cihelka, J. and Civiš, S. A High-Power Laser-Driven Source of Sub-nanosecond Soft X-Ray Pulses for Single-Shot Radiobiology Experiments. Radiat. Res. 168, 382–387 (2007). A large-scale, double-stream gas puff target has been illuminated by sub-kJ, near-infrared (NIR) focused laser pulses at the PALS facility (Prague Asterix Laser System) to produce high-energy pulses of soft X rays from hot, dense plasma. The double-puff arrangement ensures high gas density and conversion efficiency from NIR to X rays approaching that typical for solid targets. In addition, its major advantage over solid targets is that it is free of debris and has substantially suppressed charged-particle emission. The X-ray emission characteristics of the source were determined for a range of gases that included krypton, xenon, N2, CO and N2-CO. A demonstrated application of the xenon-based source is a single-shot damage induction to plasmid DNA. The yields of single-strand breaks (SSBs) and double-strand breaks (DSBs) were determined as a function of energy fluence adjusted by varying distance of sample from the source and thickness of aluminum filters.

Molecular crystals of 2-amino-1,3,4-thiadiazole with inorganic oxyacids – crystal engineering, phase transformations and NLO properties

Eight inorganic salts of 2-amino-1,3,4-thiadiazole (2-athd) with hydrochloric, perchloric, nitric, sulphuric, selenic, phosphorous and phosphoric acids were prepared, and their crystal structures were determined. Seven of the compounds crystallise in monoclinic space groups – i.e., 2-athd(1+) chloride monohydrate (P21/c), 2-athd(1+) selenate monohydrate (Pc), 2-athd(1+) dihydrogen phosphate (Cc), 2-athd(1+) phosphite (P21/a), 2-athd(1+) nitrate (P21/c), 2-athd(1+) 2-athd perchlorate (P21/n) and 2-athd(1+) perchlorate (P21/c) – and one crystallises in an orthorhombic space group – 2-athd(1+) hydrogen sulphate (P212121). The thermal behaviours of the materials were studied (DSC) down to liquid nitrogen temperature, and the properties of the perchlorate, hydrogen sulphate and selenate monohydrate crystals were discussed with respect to the results of high or low-temperature X-ray diffraction, IR and Raman spectroscopic studies. Quantitative measurements of the second harmonic generation of the powdered non-centrosymmetric samples at 1064 and 800 nm were performed and a relative efficiency compared to KDP is presented.

Tris(2-amino-1,3-thia-zolium) hydrogen sulfate sulfate monohydrate.

The centrosymmetric crystal structure of the novel semi-organic compound, 3C3H5N2S+·HSO4 −·SO4 2−·H2O, is based on chains of alternating anions and water molecules (formed by O—H⋯O hydrogen bonds). The chains are interconnected with the 2-amino-1,3-thiazolium cations via strong N—H⋯O and weak C—H⋯O hydrogen-bonding interactions into a three-dimensional network.

Ablation of Organic Molecular Solids by Focused Soft X-Ray Free-Electron Laser Radiation

The first soft X-ray free-electron laser has recently been put into operation at DESY in Hamburg. Tunable soft X-ray coherent radiation can be generated at the FLASH (Free-electron LASer in Hamburg; formerly known as VUV FEL or TTF2 FEL). In the interaction experiments reported here, the laser system provided ~ 25-fs, ~ 10-μ J pulses of 32-nm radiation. We irradiated thin (500 nm) layers of poly (methyl methacrylate) – PMMA deposited on a silicon substrate by single, focused FLASH pulses. The pulse energy was adjusted using a gas attenuator.

2-Amino-1,3-thia­zolium dihydrogen phosphate

In the title compound, C3H5N2S+·H2PO4 −, the dihydrogen phosphate anions form infinite chains along [001] via short O—H⋯O hydrogen bonds. The 2-aminothiazolium cations interconnect these chains into a three-dimensional network by short linear or bifurcated N—H⋯O and weak C—H⋯O hydrogen bonds.

Optical emission spectroscopy of various materials irradiated by soft x-ray free-electron laser

The beam of Free-Electron Laser in Hamburg (FLASH) tuned at either 32.5 nm or 13.7 nm was focused by a grazing incidence elliptical mirror and an off-axis parabolic mirror coated by Si/Mo multilayer on 20-micron and 1-micron spot, respectively. The grazing incidence and normal incidence focusing of ~10-fs pulses carrying an energy of 10 μJ lead at the surface of various solids (Si, Al, Ti, Ta, Si3N4, BN, a-C/Si, Ni/Si, Cr/Si, Rh/Si, Ce:YAG, poly(methyl methacrylate) - PMMA, stainless steel, etc.) to an irradiance of 1013 W/cm2 and 1016 W/cm2, respectively. The optical emission of the plasmas produced under these conditions was registered by grating (1200 lines/mm and/or 150 lines/mm) spectrometer MS257 (Oriel) equipped with iCCD head (iStar 720, Andor). Surprisingly, only lines belonging to the neutral atoms were observed at intensities around 1013 W/cm2. No lines of atomic ions have been identified in UV-vis spectra emitted from the plasmas formed by the FLASH beam focused in a 20-micron spot. At intensities around 1016 W/cm2, the OE spectra are again dominated by the atomic lines. However, a weak emission of Al+ and Al2+ was registered as well. The abundance ratio of Al/Al+ should be at least 100. The plasma is really cold, an excitation temperature equivalent to 0.8 eV was found by a computer simulation of the aluminum plasma OE spectrum. A broadband emission was also registered, both from the plasmas (typical is for carbon; there were no spectral lines) and the scintillators (on Ce:YAG crystal, both the luminescence bands and the line plasma emission were recorded by the spectrometer).