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In this work, we present the results of the analysis performed with near edge absorption fine structure spectroscopy of barium edges in a B+BaF2 optical filter. The radiation was generated by a laser-plasma soft X-ray source based on a double-stream gas puff target. The use of a flat-field spectrometer based on a diffraction grating allowed us to collect the absorption spectra of the radiation transmitted by the analyzed optical filter. The results demonstrate the appearance of clear M-edges of barium (M4 and M5). [ABSTRACT FROM AUTHOR]

The term "laser microexplosion" has been introduced to stress the violent character of the optical breakdown by laser radiation under conditions of tight focusing. Generally, the starting phase of the breakdown has been neglected by the assumption of absorption triggered by the presence of damage precursors. The application of the plasticity–elasticity theory in the analysis of the dynamics of this phenomenon has not been extensively examined to date. This paper formulates a phenomenological model attempting to explain the creation of nanovoids in a soft matter under irradiation by a flux of extreme ultraviolet (XUV)/soft x-ray photons. The combined action of plastic deformation and dissociation waves on soft matter is found to be responsible for the material modifications. It is suggested that localized (volume ≃ λ 3) abundance of energy, coming most likely from photon bunching, constitutes the real onset of the photo-ablative decomposition. It is shown that the coincidental presence of some small number of energy carriers (2–3 XUV photons in the considered case) in such a small volume triggers processes denoted from now on as a laser nanoexplosion. The effect is considered to be the first step in the optical breakdown followed by an intense material removal resembling, to some extent, a phase explosion. [ABSTRACT FROM AUTHOR]

Low-temperature plasma production is possible as a result of photoionization using high-intensity extreme ultraviolet (EUV) and soft X-ray (SXR) pulses. Plasma of this type is also present in outer space, e.g., aurora borealis. It also occurs when high-velocity objects enter the atmosphere, during which period high temperatures can be produced locally by friction. Low-temperature plasma is also formed in an ambient gas surrounding the hot laser-produced plasma (LPP). In this work, a special system has been prepared for investigation of this type of plasma. The LPP was created inside a chamber filled with a gas under a low pressure, of the order of 1–50 mbar, by a laser pulse (3–9 J, 1–8 ns) focused onto a gas puff target. In such a case, the SXR/EUV radiation emitted from the LPP was partially absorbed in the low-density gas. In this case, high- and low-temperature plasmas (Te ~100 eV and ~1 eV, respectively) were created locally in the chamber. Investigation of the EUV-induced plasmas was performed mainly using spectral methods in ultraviolet/visible (UV/VIS) light. The measurements were performed using an echelle spectrometer, and additionally, spatial–temporal measurements were performed using an optical streak camera. Spectral analysis was supported by the PGOPHER numerical code.

In this work, low-temperature photoionized plasma, induced in N2 by extreme ultraviolet (EUV) pulses, was used for surface modification of poly(L-lactic acid) (PLLA). Polymer samples were irradiated with 100, 200, and 300 pulses at a 10 Hz repetition rate. The physical and chemical properties of PLLA samples were examined using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The human dermal fibroblast adult cells (NHDF-Ad) were used for the cell culture and viability tests on modified PLLA surfaces. The N2-plasma and EUV treatment caused alteration of the surface morphology resulting in increased surface roughness, incorporation of nitrogen atoms, and appearing of new functional groups on the surface. Cell culture results showed an increase in the number of fibroblasts attached to the modified surfaces compared to the pristine PLLA. The modified surfaces demonstrated high cell viability and no cytotoxic effects were observed. [ABSTRACT FROM AUTHOR]

We present results of applying a compact laboratory system based on a laser-plasma soft X-ray (SXR) source to the extended X-ray absorption fine structure (EXAFS) spectroscopy of titanium in the vicinity of the LIII absorption edge. The source, operating with a plasma produced as a result of irradiation a krypton/helium double-stream gas-puff target, was optimized for an intense emission in the spectral range between 200 and 700 eV. A broad SXR spectrum and high photon flux are indispensable in the EXAFS studies. The experimental setup assured the simultaneous acquisition of both the reference and the absorption spectra. A grazing-incidence flat-field spectrometer was used to record the spectra. The absorption spectra of a thin (200-nm thick) titanium sample revealed the features in the EXAFS region allowing for quite accurate determination of the radial distances between the atoms. Results are in good agreement with the output of numerical modeling based on photoelectron wave function scattering and with the data reported for using a synchrotron source. This confirms the suitability of the source for using it in the standard EXAFS method. [ABSTRACT FROM AUTHOR]

Interaction of extreme ultraviolet (EUV) pulses of high intensity with gases results in the creation of non-thermalized plasmas. Energies of the driving photons and photoelectrons are sufficient for creation of excited states, followed by emission of the EUV photons. In most cases, decay times of these states are short comparing to the driving EUV pulse. It means that just after stopping of the driving pulse, the EUV emission corresponding to the excited states should also stop. From our earlier measurements in the optical range, however, it can be concluded that lifetimes of such plasmas exceed a time duration of the driving pulse even two orders of magnitude. Hence, it can be expected that the time duration of the EUV emission can be also significantly longer than the irradiation time. In this work, EUV-induced, low-temperature helium (He), krypton, and xenon plasmas were investigated. EUV emission from these plasmas was studied, using a specially prepared detection system, allowing for time-resolved measurements, in selected spectral ranges. The detection system was based on a paraboloidal collector and a semiconductor photodiode, sensitive for the EUV photons. For spectral selection, the corresponding filters or multilayer mirrors were employed. In most cases, the time duration of the EUV emission was significantly longer than the driving EUV pulse. In case of He plasmas, the emission corresponding to excited atoms was detected even hundreds of nanoseconds after the irradiation. It was also shown that the corresponding time profiles depended on densities of gases to be ionized. [ABSTRACT FROM AUTHOR]

Irradiation of gases with intense pulses of extreme ultraviolet (EUV) can result in the formation of low-temperature plasmas. During the time of irradiation, various non-thermal processes driven by the EUV photons and photoelectrons take place, leading to the creation of excited states of atoms and ions. Fast relaxation of these states should result in EUV emission within a time comparable to the driving EUV pulse. On the other hand, from our earlier works, a time duration of the emission in an optical range is over an order of magnitude longer. It can be thus expected that the time of EUV emission can be also relatively long. In this work, time-resolved measurements of the EUV emission from low-temperature plasmas induced in He, Ne, and Ar gases were performed. Due to a low intensity of the emitted radiation, a specially prepared detection system, based on an EUV collector and an EUV sensitive photodiode, was employed. In all cases, a time duration of the EUV emission was much longer compared with the driving EUV pulse. Time profiles of the corresponding signals were specific for particular gases. In case of He and Ne plasmas, these time profiles varied with initial densities of gases to be ionized. The corresponding dependence was especially visible in case of plasmas induced in helium. In case of Ar plasmas, such dependence was not revealed. [ABSTRACT FROM AUTHOR]

In this work, extreme ultraviolet (EUV) emission, from EUV induced, low-temperature microplasmas, were investigated. To perform temporal measurements of the EUV pulses of low intensity, in a medium vacuum, under the pressure of the order of 0.1–0.01 mbar a special detection system was prepared. The system was based on an EUV collector and a semiconductor detector, sensitive for the EUV photons. The collector consisted of two identical grazing incidence, paraboloidal mirrors, and allowed to focus a part of the radiation emitted from the microplasma onto the detector surface. An absorption filter, mounted between the collector and the detector, allowed for selection of an interesting wavelength range. Plasmas were created by irradiation of small portions of gases, injected into the vacuum chamber, using a laser produced plasma EUV source. Three gases were used for the EUV induced plasma formation: neon, krypton, and xenon. Low-temperature plasmas, created in these gases, contained multiply charged ions, emitting radiation in similar wavelength ranges. Two detectors, AXUV20HS1 and AXUVHS5, were used for the measurements. It was shown that differences between the corresponding signal profiles, obtained using both detectors, were not very significant. Moreover, it was demonstrated that the duration of the EUV emission from plasmas, created in different gases, were comparable with the duration of the driving EUV pulse. The longest EUV emission was observed for Kr plasmas, approximately 1.5 times the full width half maximum of the driving EUV pulse. [ABSTRACT FROM AUTHOR]

In this work, a comparative study of extreme ultraviolet (EUV) induced low temperature SF6-based plasmas, created using two different irradiation systems, was performed. Both systems utilized laser-produced plasma (LPP) EUV sources. The essential difference between the systems concerned the formation of the driving EUV beam. The first one contained an efficient ellipsoidal EUV collector allowing for focusing of the EUV radiation at a large distance from the LPP source. The spectrum of focused radiation was limited to the long-wavelength part of the total LPP emission, λ > 8 nm, due to the reflective properties of the collector. The second system did not contain any EUV collector. The gas to be ionized was injected in the vicinity of the LPP, at a distance of the order of 10 mm. In both systems, energies of the driving photons were high enough for dissociative ionization of the SF6 molecules and ionization of atoms or even singly charged ions. Plasmas, created due to these processes, were investigated by spectral measurements in the EUV, ultraviolet (UV), and visible (VIS) spectral ranges. These low temperature plasmas were employed for preliminary experiments concerning surface treatment. The formation of pronounced nanostructures on the silicon surface after plasma treatment was demonstrated. [ABSTRACT FROM AUTHOR]