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Irradiation of any gas with an intense EUV (extreme ultraviolet) radiation beam can result in creation of photoionized plasmas. The parameters of such plasmas can be significantly different when compared with those of the laser produced plasmas (LPP) or discharge plasmas. In this work, the photoionized plasmas were created in a krypton gas irradiated using an LPP EUV source operating at a 10 Hz repetition rate. The Kr gas was injected into the vacuum chamber synchronously with the EUV radiation pulses. The EUV beam was focused onto a Kr gas stream using an axisymmetrical ellipsoidal collector. The resulting low temperature Kr plasmas emitted electromagnetic radiation in the wide spectral range. The emission spectra were measured either in the EUV or an optical range. The EUV spectrum was dominated by emission lines originating from Kr III and Kr IV ions, and the UV/VIS spectra were composed from Kr II and Kr I lines. The spectral lines recorded in EUV, UV, and VIS ranges were used for the construction of ...

An investigation was made of a plasma formed by heating a gas target with neodymium gas laser radiation of ~15 GW power. The working substance was gaseous SF6. The x-ray emission spectra of sulfur and fluorine ions were investigated with one- and two-dimensional spatial resolution. These spectra were recorded by a high-resolution high-luminosity spectrograph with a mica crystal bent to form a sphere with a radius of R = 10 cm. Laser breakdown of a gas puff produced a sufficiently compact near-spherical plasma formation of ~2.5 mm size and with the electron temperature at least 470 eV.

In this work spectral investigations of low temperature F-rich photoionized plasmas were performed. The photoionized plasmas were created by irradiation of SF6 gas with intense EUV (extreme ultraviolet) radiation pulses. Two laser plasma EUV sources of different parameters used in the experiments were based on 0.8 J /4ns and 10 J/ 10 ns Nd:YAG lasers respectively. Both sources operated at 10 Hz repetition rate. The EUV radiation was focused using a dedicated reflective collector onto the gas stream, injected into a vacuum chamber synchronously with the EUV pulses. Irradiation of the SF6 gas resulted in dissociative ionization of the molecules, leading to creation of SFn+ ions and fluorine atoms. Further photo- or electron impact ionization and excitation processes allow for formation of photoionized plasmas emitting radiation in the wide spectral range. Emission spectra were measured in the EUV and optical ranges. The EUV spectra contained multiple spectral lines, originating from F II, F III and S II ions. The UV/VIS spectra were composed of spectral lines corresponding to radiative transitions in F II, F I and S II species. A computer simulation of the F II spectrum was performed using a collisional-radiative PrismSPECT code. Parameters of the photoionized plasmas were estimated by fitting the spectrum obtained from the simulations to the experimental one. Apart from that, the electron temperature was estimated employing Boltzmann plots based on the UV/VIS spectrum.

In this work we present a short review of SXR and EUV optics that have been designed and developed for experiments concerning material processing and imaging, using a laser-plasma radiation source based on a gas puff target. Three different kinds of mirrors employed as the EUV collectors are presented: the grazing incidence axisymmetrical ellipsoidal mirror, the grazing incidence multifoil mirror, and the ellipsoidal mirror with Mo/Si multilayer coating. Experiments concerning characterization of the mirrors were performed using EUV radiation from Kr or Xe plasmas produced in a double stream gas puff target irradiated with Nd:YAG laser pulses (4ns, 0.8 J, 10 Hz). Intensity of the focused radiation was sufficient for micromachining of organic polymers and surface modification of organic and inorganic solids. Different kinds of micro-and nanostructures created in near-surface layers of different kinds polymers were obtained. Significant differences were revealed in XPS spectra acquired for irradiated and not irradiated polymers.

High resolution imaging methods and techniques are currently under development. One of them is an extreme ultraviolet (EUV) microscopy, based on Fresnel zone plates. In this paper a compact, high-repetition, laser-plasma EUV source, emitting quasi-monochromatic radiation at 13.8nm wavelength was used in a desktop EUV transmission microscopy with a spatial (half-pitch) resolution of 50nm. EUV microscopy images of objects with various thicknesses and the spatial resolution measurements using the knife-edge test are presented.

High-current nanosecond discharges through metal wires and insulator fibres were investigated in the NIKE-3 (100 kA, 50 ns) and BIN (250 kA, 100 ns) facilities. Glass fibres were used as an example in a study of the dependence of the discharge conditions on the linear density μ of the load. An increase in μ altered the nature of the discharge through the diode from a mismatched regime accompanied by generation of an electron beam (μ 30 μg cm-1). A strong influence of the state of the surface on the nature of an explosion of a metal wire was observed. The experimental results obtained at the beginning of wire explosions were accounted for by a model of the metal—plasma transition. The plasma motion and the development of instabilities of a plasma filament during a discharge were investigated by optical methods. Some of the experiments indicated simultaneous development of helical and 'sausage' instabilities. A two-dimensional ideal magnetohydrodynamic model was employed in calculations dealing with the process of formation of a constriction (pinching) and the results were in good agreement with the observations.

Guided propagation of intense 28 fs laser pulses through a long gas jet made it feasible to produce a bright 27th harmonic from argon with a divergence of 0.5 mrad. This harmonic saturated an x-ray charge-coupled device of an extreme ultraviolet spectrometer in a single laser shot of 5 mJ. The low-divergence harmonic generation resulted from a well-guided pumping laser pulse, achieved by balancing diffraction and plasma defocusing with nonlinear self-focusing, and a large harmonic-generation cross section.

In this paper we report a desk-top microscopy reaching 50 nm spatial resolution in very compact setup using a gas-puff laser plasma EUV source. The thickness of an object and the bandwidth of illuminating radiation were studied in order to estimate their quantitative influence on the EUV microscope spatial resolution. EUV images of various thickness objects obtained by illumination with variable bandwidth EUV radiation were compared in terms of knife-edge spatial resolution to study the bandwidth/object thickness parasitic influence on spatial resolution of the EUV microscope.

In this work results of investigations concerning ablation and surface modification of polymers and some other solids using a laser-plasma EUV source are presented. The plasma radiation was produced using a gas puff target and was focused with a gold-plated grazing incidence ellipsoidal collector. The ablation process was investigated using a scanning electron microscope (SEM) and a quadrupole mass spectrometer (QMS). The chemical changes were investigated by X-ray photoelectron spectroscopy (XPS). Different kinds of micro- and nanostructures created in nearsurface layers of the materials were obtained. Forms of the structures depend on a particular material and the EUV exposure. In case of some polymers even a single shot was sufficient for creation of the visible changes in surface morphology. In case of inorganic solids visible changes required usually the exposure with tens or hundreds of EUV pulses. XPS investigations revealed chemical changes in near surface layers of polymers. Significant differences were revealed in the XPS spectra acquired for irradiated and not-irradiated polymers. Significant decrease of functional groups containing oxygen was indicated. Analysis of QMS spectra indicate emission of different kinds of fragments of the polymer chains including the repeating structural units. In case of some polymers only fragments of the repeating unit were detected.

In this paper the recent advancements in technology of compact laser plasma EUV sources based on a gas puff target are presented. These sources have been used in nanoimaging and micro- and nanoprocessing polymers.

Experiments with electric discharges across hollow gaseous envelopes have been carried out on a microsecond plasma generator of x radiation (200 kA, 40 kV, 1.5 μs, Ne–Ar mixture). The diagnostic complex made it possible to carry out time- and space-resolved observations in the visible range by means of streak and framing cameras. In the vacuum-UV range, a spectrograph with a transparent grating and a vacuum x-ray diode were used. In the soft x-ray range, a crystal spectrograph with convex and spherically bent crystals, a crystal x-ray microscope, pinhole cameras, and p-i-n diodes were used. The spectral range 0.3–1.5 nm contains lines of He- and H-like Ne and of He-like Ar. These ions are used for x-ray-spectral estimates of the electron temperatures and the densities of the plasma of the hot spots. These estimates lie in the ranges 1–1.3 keV and (0.5–1) 1022 cm−3. At the optimum nozzle diameter in terms of the x-ray yield, a kink instability and the formation of hot spots are observed simultaneously. Suppressing the kink instability increases the radiation yield. Emission from the plasma column in Kα lines of argon has been observed.

Decreasing the illumination wavelength provides the potential to improve the spatial resolution in all imaging techniques. Hence there is currently high interest in imaging using laboratory short wavelength sources. This chapter describes approaches to EUV imaging utilizing a compact table-top capillary discharge EUV laser. Various coherent imaging techniques, such as two and three dimensional holography, computer generated holograms (CGHs), EUV reconstruction and generalized Talbot self-imaging will be presented.

We report the first (to our knowledge) demonstration of a tabletop, extreme UV (EUV) transmission microscope at 13.8 nm wavelength with a spatial (half-pitch) resolution of 69 nm. In the experiment, a compact laser-plasma EUV source based on a gas puff target is applied to illuminate an object. A multilayer ellipsoidal mirror is used to focus quasi-monochromatic EUV radiation onto the object, while a Fresnel zone plate objective forms the image. The experiment and the spatial resolution measurements, based on a knife-edge test, are described. The results might be useful for the realization of a compact high-resolution tabletop imaging systems for actinic defect characterization.

The recent advancements in technology of compact laser plasma EUV sources based on a gas puff target are presented in the paper. The sources have been developed for application in processing materials using EUV radiation in the wavelength range from about 5 nm to about 50 nm that is efficiently produced in result of irradiation a double-stream gas puff target with high-intensity laser pulses from a Nd:YAG laser (0.8 J/4 ns/10 Hz). The sources can be equipped with two various grazing incidence optical systems to focus EUV radiation: an axisymmetrical ellipsoidal mirror or a multifoil mirror system of the "lobster eye" type. A new design of the laser plasma EUV source dedicated for micro- and nanoprocessing polymers and modification of polymer surfaces is presented for the first time.

We report on the application of a compact laser plasma EUV source for processing of polymer materials. The EUV radiation in the wavelength of about 5 to 50 nm was produced by irradiation of xenon or krypton gas puff target with Nd:YAG laser operating at 10 Hz and delivering 4 ns pulses of energy up to 0.8 J per pulse. The source was equipped with a grazing incidence axisymmetrical ellipsoidal mirror to focus EUV radiation in the relatively broad spectral range with the maximum near 10 nm. The size of the focal spot was about 0.5 mm with the maximum fluence of 70 mJ/cm2 in a single pulse. Nanostructuring of polymer materials was achieved, primarily due to direct photo-etching with EUV photons. The results of the studies should be applicable in biomedical engineering.

The control of cell adhesion at polymer surfaces is of great interest for applications in medicine and biotechnology research.We present a method of polystyrene (PS) surface treatment by UV laser irradiation (laser wavelength λ=193 nm) for the improvement of adhesion of Chinese hamster ovary (CHO) cells.We irradiated the PS foils with a total fluence of 200 mJ/cm2 in a circular spot. The irradiation led to formation of specific micro pattern at the surface (assessed by AFM and SEM). Depending on the position at the spot, the pattern structure varies. There is a specific ring area (B in figure), where seeded CHO cells show effective adhesion and pronounced spreading. The cells display here a preferential alignment along the ring. The topography of this area has a height variation of 5 to 10 nm, while the surface region irradiated with higher laser intensity (A in figure) has a higher roughness of hundreds of nm. This area is less favorable for CHO cells adhesion as indicated by the round cell morphology, similar to the flat area outside the ring. (Supported by the Austrian NANO Initiative in the projects NSI_NBPF and NSI_PolyModEUV.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Extreme ultraviolet (EUV) is strongly absorbed in any materi al and can be transmitted only through very thin foils. The material surface after irradiation can remain unchanged or becomes modified in some way depending on radiation fluence and material properties. In so me materials the surface changes may aris e due to fast melting or boiling followed by solidification. In other cases photochemical or photothermal ablation can occur. It requires relatively high radiation fluence of the order of tens mJ/cm 2 . A laser-plasma EUV source based on a gas pu ff target equipped with a proper optic can deliver such conditions. In this work EUV radiation coming from xenon or krypton plasma was focused using an ellipsoidal grazing incidence collector. Different kind of material samples were irradiated in the focal plane or at some distance behind the focal plane. This way different intensitie s were applied for irradiation of the samples. Irradiation was performed with 10 Hz repetition rate and different time duration varying from 1s to 2 min. Surface morphology after irradiation was investigated using a scanni ng electron microscope. In a case of so me materials EUV intensity in the focal plane was sufficient for ablation. In other cases material ablation was not possible but surface structure was modified. Forms of the structures for a certain material depend both on EUV fluence in a single shot and the number of shots. Keywords: laser-plasma, EUV, gas puff target , photo-etching, surface modification

In this paper some results of investigations concerning interaction of EUV radiation with inorganic and organic materials were presented. Samples of different materials were irradiated with a 10 Hz laser - plasma EUV source based on a gas puff target. The source was equipped with grazing incidence and multilayer collecting mirrors. The grazing incidence collector was used in experiments concerning surface modification and micromachining of different materials. The micromachining experiments were performed for different polymers that were irradiated through a fine metal grid as a contact mask. For fluoropolymers, EUV radiation with fluence of 10 mJ/cm 2 was enough for efficient photo-etching. The photo-etching speed was maximal for polytetrafluoroethylene (PTFE) reaching 30nm per shot. It was shown that using such a method microstructures with high aspect ratio could be produced. Experiments connected with surface modification were performed either with organic or inorganic materials. Different kinds of surface structures were obtained depending on irradiated materials and irradiation parameters. The Mo/Si collector together with argon plasma was used for obtaining a quasi-monochromatic radiation for EUV microscopy and some metrological applications.

We demonstrate a neonlike argon-ion x-ray laser, using a short-pulse laser-irradiated gas puff target. The gas puff target was formed by pulsed injection of gas from a high-pressure solenoid valve through a nozzle in the form of a narrow slit and irradiated with a combination of long, 600-ps and short, 6-ps high-power laser pulses with a total of 10 J of energy in a traveling-wave excitation scheme. Lasing was observed on the 3p (1)S(0)?3s (1)P(1) transition at 46.9 nm and the 3d (1)P(1)?3p (1)P(1) transition at 45.1 nm. A gain of 11 cm(-1) was measured on these transitions for targets up to 0.9 cm long.

Results on micro- and nanoprocessing of organic polymers with extreme ultraviolet (EUV) radiation from a compact laser plasma EUV source based on a gas puff target are presented in the paper. Processing of polymers is connected with non-thermal ablation under the influence of energetic EUV photons. The process can be useful for practical applications as it makes possible to produce structures with sub-micron spatial resolution that is not possible using the thermal ablation. The new technology will be used for production of photonic microstructures and for modification of polymer surfaces for biomedical applications.

A single photon of EUV radiation carries enough energy to break any chemical bond or excite electrons from inner atomic shells. It means that the radiation regardless of its intensity can modify chemical structure of molecules. It is the reason that the radiation even with low intensity can cause fragmentation of long chains of organic materials and desorption of small parts from their surface. In this work interaction of EUV radiation with inorganic materials was investigated. Different inorganic samples were irradiated with a 10 Hz laser - plasma EUV source based on a gas puff target. The radiation was focused on a sample surface using a lobster eye collector. Radiation fluence at the surface reached 30 mJ/cm 2 within a wavelength range 7 - 20 nm. In most cases there was no surface damage even after several minutes of irradiation. In some cases there could be noticed discolouration of an irradiated surface or evidences of thermal effects. In most cases however luminescent and scattered radiation was observed. The luminescent radiation was emitted in different wavelength ranges. It was recorded in a visible range of radiation and also in a wide wavelength range including UV, VUV and EUV. The radiation was especially intense in a case of non-metallic chemical compounds.

In this work, photoionized plasmas were created by irradiation of gaseous argon with soft x-ray (SXR) and extreme ultraviolet (EUV) intense radiation pulses. Two different laser-produced plasma sources, employing a low energy Nd:YAG laser and a high energy iodine laser system (PALS), were used for creation of photoionized plasmas. In both cases the EUV or SXR beam irradiated the Ar stream, injected into a vacuum chamber synchronously with the radiation pulse. Emission spectra, measured for the Ar photoionized plasmas indicated strong differences in ionization degree for plasmas produced using low and high energy systems. In case of the the EUV driving pulses, emission lines corresponding to neutral atoms and singly charged ions were observed. In case of the SXR pulses utilized for the photoionized plasma creation, only Ar V–VIII emission lines were recorded. Additionally, electron density measurements were performed by laser interferometry employing a femtosecond laser system synchronized with the irradiating system. Maximum electron density for the Ar photoionized plasma, induced using the high energy system, reached 1.9 1018 cm−3. Interferometric measurements performed for the moment of maximum intensity of the main laser pulse (t = 0) revealed no fringe shift. Detection limit for the interferometric measurements was estimated. It allowed to estimate the upper limit for electron density at t = 0 as 5 1016 cm−3.

Microscopes operating at short wavelengths, in the extreme ultraviolet and soft x-ray spectral region, require careful condenser positioning to avoid possible artifacts related to enhancing or diminishing certain spatial frequencies in the image plane. Various methods are often used to visualize the condenser illumination pattern, including direct visualization on a CCD camera; however, these are not always straightforward to use. We present and discuss a novel and convenient method to image a condenser illumination pattern upstream the sample plane, using two zone plates with matched numerical apertures. This imaging system, operating herein in the water-window spectral range in telescope configuration, allows us to change the distance between the conjugated planes, thus overcoming limitations related to the geometry of the vacuum system. This geometry, which is optimized for the highest possible spatial resolution allowed by the zone-plate objective, is not necessarily particularly good for visualization of the condenser illumination pattern. The presented method was demonstrated with a compact, gas puff target source based soft x-ray microscope, which is capable of resolving 60 nm features (half-pitch resolution), requires a few seconds exposure time, and is debris-free due to the gaseous nature of the target for soft x-ray generation. The method, presented herein, may solve mentioned vacuum system geometry limitations. Also, it can easily be extended to other systems and other wavelengths, provided a proper optic is used. Modes of operation and the results are presented and discussed.

A comparative study of photoionized plasmas created by two soft X-ray and extreme ultraviolet (SXR/EUV) laser plasma sources with different parameters is presented. The two sources are based on double-stream Xe/He gas-puff targets irradiated with high (500 J/0.3 ns) and low energy (10 J/1 ns) laser pulses. In both cases, the SXR/EUV beam irradiated the gas stream, injected into a vacuum chamber synchronously with the radiation pulse. Irradiation of gases resulted in formation of photoionized plasmas emitting radiation in the SXR/EUV range. The measured Ne plasma radiation spectra are dominated by emission lines corresponding to radiative transitions in singly charged ions. A significant difference concerns origin of the lines: K-shell or L-shell emissions occur in case of the high and low energy irradiating system, respectively. In high energy system, the electron density measurements were also performed by laser interferometry, employing a femtosecond laser system. A maximum electron density for Ne plasm...

Davidkova, M., Juha, L., Bittner, M., Koptyaev, S., Krasa, J., Pfeifer, M., Stisova, V., Bartnik, A., Fiedorowicz, H., Mikolajczyk, J., Ryc, L., Pina, L., Horvath, M., Babankova, D., Cihelka, J. and Civis, 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 ...

Investigations of emission of harmonics from argon gas jet irradiated by 700 fs, 5 mJ pulses from a KrF laser are presented. Harmonics conversion was optimized by varying the experimental geometry and the nozzle size. For the collection of the harmonic radiation silicon and solar-blind diamond semiconductor detectors equipped with charge preamplifiers were applied. The possibility of using a single-crystal CVD diamond detector for separate measurement of the 3rd harmonic in the presence of a strong pumping radiation was explored. Our experiments show that the earlier suggested 0.7% conversion efficiency can really be obtained, but only in the case when phase matching is optimized with an elongated gas target length corresponding to the length of coherence.

Organic polymers (PMMA, PTFE, PET, and PI) are considered as the important materials in microengineering, especially for biological and medical applications. Micromachining of such materials is possible with the use of different techniques that involve electromagnetic radiation or charged particle beams. Another possibility of high aspect ratio micromachining of PTFE is direct photo-etching using synchrotron radiation. X-ray and ultraviolet radiation from other sources, for micromachining of materials by direct photo-etching can be also applied. In this paper we present the results of investigation of a wide band soft X-ray source and its application for direct photo-etching of organic polymers. X-ray radiation in the wavelength range from about 3 nm to 20 nm was produced as a result of irradiation of a double-stream gas puff target with laser pulses of energy 0.8 J and time duration of about 3 ns. The spectra, plasma size and absolute energies of soft X-ray pulses for different gas puff targets were measured. Photo-etching process of polymers irradiated with the use of the soft X-ray radiation was analyzed and investigated. Samples of organic polymers were placed inside a vacuum chamber of the x-ray source, close to the gas puff target at the distance of about 2 cm from plasmas created by focused laser pulses. A fine metal grid placed in front of the samples was used as a mask to form structures by x-ray ablation. The results of photo-etching process for several minutes exposition with l0Hz repetition rate were presented. High ablation efficiency was obtained with the use of the gas puff target containing xenon surrounded by helium.

Single ≤1 kJ pulses from a high-power laser are focused into molecular gases to create large laser sparks. This provides a unique way to mimic the chemical effects of high-energy-density events in planetary atmospheres (cometary impact, lightning) matching the natural energy-density, its spatio-temporal evolution and plasma-volume scaling of such events in a fully-controlled laboratory environment. Some chemical reactions initiated by laser-induced dielectric breakdown (LIDB) in both pure molecular gases and mixtures related to the chemical evolution of the Earth's early atmosphere were studied. Most of the experiments were carried out in a static gas cell. However, an initial series of experiments was also performed with a gas-puff target placed within a vacuum interaction chamber. Under these dynamic conditions the hot core of a laser spark can be directly investigated.

A new high-density gas puff target for experiments on laser-driven X-ray lasers is presented. The target is based on a double-stream gas puff target approach, which makes possible to form an elongated gas sheet with steep density gradient and high density of gas in the interaction region. In the paper the valve system to produce the gas puff targets and the results of the target characterization measurements performed using X-ray backlighting technique are presented.

A pulse-train Nd:YAG laser system consisting of repetitively Q-switched Nd:YAG oscillator with Cr 4+ :YAG saturable absorber, double pass Nd:YAG amplifier and stimulated Brillouin scattering (SBS) pulse compressor has been demonstrated. Number and energy of the laser pulses were controlled by adjusting width and amplitude of the flash lamp pumping pulses. Efficient SBS compression of Nd:YAG laser pulses was obtained using single-cell compressor.

Experiments on direct photo-etching of organic polymers induced by high-intensity nanosecond pulses of soft X-ray radiation from a laser plasma X-ray source based on a gas puff target are presented. X-rays in the wavelength range from about 1 nm to 8 nm were produced by irradiation of the xenon/helium double-stream gas puff target with laser pulses from the Prague Asterix Laser System (PALS). The resulting X-ray pulses were used to irradiate samples from organic polymers and form microstructures. The results show relatively high efficiency of X-ray direct photo-etching that could be useful for micromachining of organic polymers.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

For conventional wavelength (UV-Vis-IR) lasers delivering radiation energy to the surface of materials, ablation thresholds, ablation (etch) rates, and the quality of ablated structures often differ dramatically between short (typically nanosecond) and ultrashort (typically femtosecond) pulses. Various short-wavelength (l < 100 nm) lasers emitting pulses with durations ranging from ~ 10 fs to ~ 1 ns have recently been put into a routine operation. This makes it possible to investigate how the ablation characteristics depend on the pulse duration in the XUV spectral region. 1.2-ns pulses of 46.9-nm radiation delivered from a capillary-discharge Ne-like Ar laser (Colorado State University, Fort Collins), focused by a spherical Sc/Si multilayer-coated mirror were used for an ablation of organic polymers and silicon. Various materials were irradiated with ellipsoidal-mirror-focused XUV radiation (λ = 86 nm, τ = 30-100 fs) generated by the free-electron laser (FEL) operated at the TESLA Test Facility (TTF1 FEL) in Hamburg. The beam of the Ne-like Zn XUV laser (λ = 21.2 nm, τ < 100 ps) driven by the Prague Asterix Laser System (PALS) was also successfully focused by a spherical Si/Mo multilayer-coated mirror to ablate various materials. Based on the results of the experiments, the etch rates for three different pulse durations are compared using the XUV-ABLATOR code to compensate for the wavelength difference. Comparing the values of etch rates calculated for short pulses with those measured for ultrashort pulses, we can study the influence of pulse duration on XUV ablation efficiency. Ablation efficiencies measured with short pulses at various wavelengths (i.e. 86/46.9/21.2 nm from the above-mentioned lasers and ~ 1 nm from the double stream gas-puff Xe plasma source driven by PALS) show that the wavelength influences the etch rate mainly through the different attenuation lengths.

In the paper a newly developed compact laser plasma EUV source is presented. The source is based on the double-stream gas puff target approach. The targets are formed by pulsed injection of high-Z gas (xenon) into a hollow stream of low-Z gas (helium) using the valve system composed of two electromagnetic valves and equipped with the double-nozzle setup. The outer stream of gas confines the inner stream improving the gas puff target characteristics (higher density of high-Z gas at longer distance from the nozzle output). It causes efficient absorption of laser energy in a plasma and strong EUV production. The source has been developed in the frame of the EUV sources development project under the MEDEA+ program.

Spectral measurements of a laser-produced soft x-ray and EUV source based on a double-stream gas puff target are described. The target was irradiated with a Nd:glass laser producing 1 ns pulses with energy up to 10 J. Production in the wavelength range up to 20 nm (x-ray and EUV emissions) have been measured from xenon, krypton, argon, and nitrogen targets using the transmission grating spectrometer with the back-illuminated CCD. Spectral characteristics of x-ray and EUV emissions are presented.

Laser-produced plasmas have been attractive compact sources of intense soft X-ray radiation applicable to various fields of researches, such as X-ray lithography, X-ray microscopy, atomic physics, and material science. The laser-produced plasma source consists of a laser system which produces high power radiation and a target that is placed inside a vacuum chamber to decrease strong absorption of soft X-rays in the air. The gas puff target is produced by pulsed injection of gas through a nozzle of a high-pressure valve into the vacuum chamber. The use of a fast acting electromagnetic valve allows creation of a high gas density region above the nozzle, and results in efficient absorption of the laser light and intense emission of X-rays comparable to the emission from a solid target.

By traveling wave irradiation with a compact, 2‐beam, 1‐ps, 20‐J CPA Nd‐glass laser dedicated to x‐ray laser research, saturated amplification has been demonstrated in Ni‐like Ag at 13.9 nm and Ni‐like Sn at 12.0 nm. High gain amplification has been also obtained in Ni‐like La at 8.8 nm and with gaseous targets in Ne‐like Ar at 46.9 nm and Ni‐like Xe at 9.98 nm. Generation of highly coherent x‐ray laser is planned by injection seeding of the plasma amplifier. The newly developed 340‐TW Ti‐sapphire laser may enable generating exceedingly high power x‐ray radiation which will be useful for pumping inner‐shell ionization x‐ray lasers.

This letter reports the first study of x‐ray emission from plasma produced by laser irradiation of gas puff targets. The gas puff targets were created by the pulsed injection of gas into a vacuum chamber. To irradiate the gas puff target a Nd‐glass laser was used, which generated 1‐ns pulses of up to 15 J in energy. Spatial, spectral, and temporal measurements show that intense soft x‐ray emission from the laser‐irradiated gas puff target is produced.

We present our recent results of a formation and characterization of plasma channels in elongated krypton and xenon gas puff targets. The study of their formation and temporal expansion was carried out using a combination of a soft X-ray radiography (shadowgraphy) and pinhole camera imaging. Two high-energy short laser pulses were used to produce the channels. When a pumping laser pulse was shaped into a line focus, using cylindrical and spherical lenses, the channels were not produced because much smaller energy density was deposited in the gas puff target. However, when a point focus was obtained, using just a spherical lens, the plasma channels appeared. The channels were up to 9 mm in length, had a quite uniform density profile, and expanded in time with velocities of about 2 cm/μs.

In this paper, results of spectral investigations of low temperature photoionized plasmas, created by irradiation of gases with intense pulses of extreme ultraviolet (EUV) radiation from a laser-produced plasma (LPP) source, are presented. The LPP source was based on a double-stream KrXe/He gas-puff target irradiated with 4 ns/0.8 J/10 Hz Nd:YAG laser pulses. The most intense emission from the source spanned a relatively narrow spectral region λ ≈ 10–12 nm; however, spectrally integrated intensity at longer wavelengths was also significant. The EUV beam was focused on a gas stream, injected into a vacuum chamber synchronously with the EUV pulses. Irradiation of gases resulted in formation of photoionized plasmas emitting radiation in the EUV range. Radiation spectra, measured for plasmas produced in various gases, are dominated by emission lines, originating from single charged ions. Significant differences in spectral intensities and distributions between plasmas created in neon and molecular gases were observed.

A combination of a ultra high vacuum arc deposition system and a recrystallization method was used to optimize the smoothness and thickness of thin-layer lead cathodes for superconducting niobium electron injectors. A non-filtered arc system was chosen to deposit Pb films on niobium. The films then underwent melting and recrystallization by treating them with pulsed argon ion beams in a rod plasma injector.

In this work photoionized plasmas were created by irradiation of He or Ne gases with a focused extreme ultraviolet (EUV) beam from one of two laser–plasma sources employing Nd:YAG laser systems. The first of them was a 10 Hz laser–plasma EUV source, based on a double-stream gas-puff target, irradiated with a 3 ns per 0.8 J laser pulse. EUV radiation in this case was focused using a gold-plated grazing incidence ellipsoidal collector. The second source was based on a 10 ns per 10 J per 10 Hz laser system. In this case EUV radiation was focused using a gold-plated grazing incidence multifoil collector. Gases were injected into the interaction region, perpendicularly to an optical axis of the irradiation system, using an auxiliary gas puff valve. Spectral measurements in the EUV range were performed. In all cases the most intense emission lines were assigned to singly charged ions. The other emission lines belong to atoms or doubly charged ions.

In this work we report our numerical modeling results of laser-generated transient inversion and capillary discharge X-ray lasers. In the search for more efficient X-ray lasers we look closely at other approaches in conjunction with experiments at LLNL. In the search for improved X-ray lasers we perform modeling and experimental investigations of low density targets including gas puff targets. We have found the importance of plasma kinetics in transient X-ray lasers by expanding the physical model beyond hydrodynamics approach with Particle In Cell (PIC) and Fokker-Planck codes. The evidence of the Langdon effect was inferred from the recent experimental data obtained with the Ni-like Pd X-ray laser. We continue modeling different kinds of capillary discharge plasma configurations directed toward shorter wavelength X-ray lasers, plasma diagnostics and other applications.

The development of the transient collisional excitation x-ray laser scheme using tabletop laser systems with multiple pulse capability has progressed rapidly in the last three years. The high small-signal gain and strong x-ray output have been demonstrated for laser drive energies of typically less than 10 J. We report recent x-ray laser experiments on the Lawrence Livermore National Laboratory (LLNL) Compact Multipulse Terawatt (COMET) tabletop facility using this technique. In particular, the saturated output from the Ni-like Pd ion 4d - 4p x-ray laser at 146.8 angstrom has been well characterized and has potential towards a useable x-ray source in a number of applications. One important application of a short wavelength x-ray laser beam with picosecond pulse duration is the study of a high density laser-produced plasma. We report the implementation of a Mach-Zehnder type interferometer using diffraction grating optics as beam splitters designed for the Ni-like Pd laser and show results from probing a 600 ps heated plasma. In addition, gas puff targets are investigated as an x-ray laser gain medium and we report results of strong lasing on the n equals 3 - 3 transitions of Ne-like Ar.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this work we demonstrate a soft x-ray laser with neon-like argon ions using a gas puff target irradiated with acombination of long 600 ps and short 6 ps high-power laser pulses with a total of 10 J energy. The gas puff target was formed by pulsed injection of gas from a high-pressure solenoid valve through a nozzle in the form of a narrow slit. Thetarget was irradiated in a travelling-wave excitation geometry. Lasing was observed on the 3p 'So —f 3s 1P1 transition at 46.9 nm and the 3d 1P1 — 3p 1P transition at 45. 1 nm. Gain of 1 1 cm' was measured on these transitions for targets upto 0.9 cm long.Keywords: x-ray lasers, laser-produced plasmas, x-ray optics, gas puff target 1. INTRODUCTION Significant progress towards the realization of a laser-driven tabletop x-ray laser has been achieved during the last few years using different variants of the prepulse technique.15 In this technique a solid target is irradiated with several laserpulses. The first pulse is used to create a large-scale length plasma, which has the appropriate density range for gain andsufficiently small density gradients for laser propagation. The subsequent pulses can be absorbed more efficiently and heatthe preformed plasma to lasing conditions. Efficient, high-brightness soft x-ray lasers with neon-like and nickel-like ions

Measurements of soft x-ray emission from a nitrogen/helium double-stream gas puff target irradiated with the Prague Asterix Laser System (PALS) have been performed. The aim of the studies was to measure the absolute yields of soft x-ray radiation in the water window from a gas puff laser plasma source and to verify the possibilities of using of this source in x-ray imaging microscopy.

Characterization measurements of a laser-produced x-ray source based on a double-stream ga puff target are presented. The target was irradiated with a Nd:glass laser producing 1 ns pulses with energy up to 10 J. Production in the wavelength range up to 200 nm have been measured form xenon, krypton, argon, and nitrogen targets using the transmission grating spectrometer with the back-illuminated CCD and the absolutely calibrated silicon photodiodes. Spectral characteristics of x-ray and EUV emissions are presented.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Generation of x-ray and extreme ultraviolet (EUV) radiation from laser-produced source with a new double-stream gas puff target has been investigated. The target was formed by pulsed injection of heavy gas (argon, or xenon) into a hollow gas stream from helium by using a double-nozzle setup. This new approach allows to form a high-density gaseous target at a relatively large distance from the nozzle output. X-ray emission was produced by irradiation of the argon/helium target with pulses of 1 ns time duration with energy up to 20 J from a Nd:glass laser. Strong x-ray emission at the wavelength near 0.4 nm from the argon target, similar to the emission from the solid sulphur target irradiated in the same conditions, have been observed. These new results may be useful to develop a laser-produced radiation source for x-ray lithography. To generate EUV radiation the xenon/helium target was irradiated using a Nd:YAG laser producing pulses of 10 ns and 0.7 J or energy. Efficient production near 11 nm from the xenon target exceeding emissions from solid targets was observed that should be useful for EUV lithography.

A double stream gas puff was proposed as a target for a laser pulse in a soft x-ray source, to overcome a problem of 3D gas flow outside the sonic nozzle. In a case of the sonic nozzle the gas density drops dramatically with a distance from the nozzle outlet. The double stream gas puff target is created by an injection of high Z gas into a hollow stream of low Z gas. Such a solution allows to decrease an x-ray absorption in cold gas and to keep the inner gas at a relatively high density on a distance up to 2mm from the nozzle outlet. Also in this case plasma emitting soft x-rays created by the laser pulse on the distance over 1mm from the nozzle outlet would not destroy it.