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Time and polarization resolved optical emission spectroscopy of laser-produced plasmas formed on Al alloys has been studied in the visible spectral range at a background air pressure of 10−4 mbar. A comparative experimental investigation has been made between the results obtained from the polarization-resolved laser-induced breakdown spectroscopy (PRLIBS) and those obtained for the unresolved case (denoted simply as LIBS here). The spectral signal-to-background ratio (SBR) is increased significantly for PRLIBS compared with LIBS for the Mn emission line at a wavelength of 415 nm, which had trace concentrations in the sample. The results have been interpreted within the framework of radiatively recombining plasma where free electrons are captured by ions to emit radiation. In addition, the degree of polarization is quantified for two matrix lines, namely Al0 (at 396.15 nm) and Al2+ (569.6 nm) by using neighbouring unpolarized emission lines. The plasma parameters are measured and compared with the degree of polarization to determine the dominant mechanism for the polarized emission. Thus, from these results, we feel confident that PRLIBS is a useful and simple addition, capable of improving experimental LIBS performance. [ABSTRACT FROM AUTHOR]

We present an overview of recent results on optical coherence tomography with the use of extreme ultraviolet and soft X-ray radiation (XCT). XCT is a cross-sectional imaging method that has emerged as a derivative of optical coherence tomography (OCT). In contrast to OCT, which typically uses near-infrared light, XCT utilizes broad bandwidth extreme ultraviolet (XUV) and soft X-ray (SXR) radiation (Fuchs et al in Sci Rep 6:20658, 2016). As in OCT, XCT's axial resolution only scales with the coherence length of the light source. Thus, an axial resolution down to the nanometer range can be achieved. This is an improvement of up to three orders of magnitude in comparison to OCT. XCT measures the reflected spectrum in a common-path interferometric setup to retrieve the axial structure of nanometer-sized samples. The technique has been demonstrated with broad bandwidth XUV/SXR radiation from synchrotron facilities and recently with compact laboratory-based laser-driven sources. Axial resolutions down to 2.2 nm have been achieved experimentally. XCT has potential applications in three-dimensional imaging of silicon-based semiconductors, lithography masks, and layered structures like XUV mirrors and solar cells. [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]

In this paper, we present the first measurements of the partial spatial coherence of the EUV emission from xenon plasma in laser-plasma source, based on a double stream gas puff target. The Young double slit approach was employed to measure complex coherence factor of the EUV Xe emission at 13.5-nm wavelength in two orthogonal directions. The radius of coherence of ~60 μm was estimated at the distance of 2.1 m from the source. The number of coherently emitted photons was sufficient to demonstrate coherent imaging. Using partially coherent radiation from such source Gabor EUV holography was successfully demonstrated. [ABSTRACT FROM AUTHOR]

A compact, desktop size microscope, based on laser-plasma source and equipped with reflective condenser and diffractive Fresnel zone plate objective, operating in the extreme ultraviolet (EUV) region at the wavelength of 13.8 nm, was developed. The microscope is capable of capturing magnified images of objects with 95-nm full-pitch spatial resolution (48 nm 25-75% KE) and exposure time as low as a few seconds, combining reasonable acquisition conditions with stand-alone desktop footprint. Such EUV microscope can be regarded as a complementary imaging tool to already existing, well-established ones. Details about the microscope, characterization, resolution estimation and real sample images are presented and discussed. [ABSTRACT FROM AUTHOR]

A volume, tomographic reconstruction of a novel, multi-jet gas puff target, developed for possible applications in high-order harmonic generation (HHG), is presented. The target, produced by pulsed injection of argon gas through nozzle in a form of linearly oriented small orifices, has been characterized in the extreme ultraviolet at 13.5 nm wavelength. Target density estimations were performed, and 3-D representation of pulsed gaseous target has been obtained by combining 2-D shadowgram images, recorded at various rotation angles. More detailed information about higher-order jets, formed as a result of collisions of primary jets, was obtained. Tomographic studies of such type of targets dedicated for HHG have been obtained to our knowledge for the first time. [ABSTRACT FROM AUTHOR]

In this paper an efficient micromachining of poly(vinylidene fluoride) (PVDF) by direct photo-etching with a laser-plasma EUV (extreme ultraviolet) source was demonstrated for the first time. Mass spectroscopy was employed to investigate the ablation products and revealed emission of numerous molecular species of C-containing fragments of the polymer chain. Chemical surface changes after irradiation were investigated using X-ray photoelectron spectroscopy (XPS). The XPS spectra obtained for PVDF samples, irradiated with low and high EUV fluence, indicate significant differences between chemical structures in near-surface layers. It was shown that irradiation with low fluence results in defluorination and thus carbon enrichment of the polymer in near-surface layer. In contrary, irradiation with high fluence leads to intense material ablation and hardly modifies the chemical structure of the remaining material. [ABSTRACT FROM AUTHOR]

In this work, the radiation from a laser-plasma extreme ultraviolet (EUV) source based on a double-stream gas-puff target was used for surface modification of polyethylene terephthalate (PET). The spectrum of the wide band radiation focused with a gold-coated ellipsoidal collector consisted of a narrow feature with maximum at 10 nm and a long-wavelength tail up to 70 nm. The PET samples were mounted in the focal plane of the EUV collector or at some distance downstream this plane and irradiated for 0.1 s-2 min with 10-Hz repetition rate. The polymer samples after irradiation were rinsed in acetone. Surface morphologies of the PET samples after irradiation were investigated using a scanning electron microscope and atomic force microscope. Different kinds of surface micro- and nanostructures were created as a result of irradiation depending on the EUV fluence and number of pulses. Acetone treatment of the polymer samples after irradiation resulted in formation of additional nanostructures. In this case the nanostructures were revealed even after exposure with a single EUV pulse. [ABSTRACT FROM AUTHOR]

In this paper a new approach to a laser-produced plasma EUV source based on a tin target is presented. A thin layer of pure tin and composite layers consisting of Sn with Si, SiO and LiF are investigated. The target composed of several thin layers produces less debris than the other targets and provides a conversion efficiency (CE) in the 13.5-nm±1% band at least comparable to the CE for the pure tin slab target. The largest CE was observed for the target composed of a mixture of Sn and LiF, due to the fact that lithium, similarly to tin, is a strong emitter at 13.5 nm. [ABSTRACT FROM AUTHOR]

The paper describes a debris-free, efficient laser-produced plasma source emitting EUV radiation. The source is based on a double-stream Xe/He gas-puff. Its properties and spectroscopic signatures are characterized and discussed. The spatio-spectral features of the EUV emission are investigated. We show a large body of results related to the intensity and brightness of the EUV emission, its spatial, temporal, and angular behavior and the effect of the repetition rate as well. A conversion efficiency of laser energy into EUV in-band energy at 13.5 nm of 0.42% has been gained. The electron temperature and electron density of the source were estimated by means of a novel method using the FLY code. The experimental data and the Hullac code calculations are compared and discussed. The source is well suited for EUV metrology purposes. The potential of the source for application in EUV lithography was earlier demonstrated in the optical characterization of Mo/Si multi-layer mirrors and photo-etching of polymers. [ABSTRACT FROM AUTHOR]

A compact, high-repetition table-top EUV source, based on a gas-puff target, is presented. This source was developed in our group and is capable of emitting quasi-monochromatic radiation at 13.8 nm wavelength with the inverse relative bandwidth of 140 and pulse energies up to ∼1.3 μJ/pulse at 10-Hz repetition rate. The source is debris-free, operates near the lithographic wavelengths and offers the energy density of ∼0.4 mJ/cm2 in each EUV pulse. These three features make the source attractive for lithographic experiments. The timing optimization of the source, its energy per pulse, spectral and spatial distributions are pointed out in detail as well as the enhancement in energy density achievable with a multi-layer collector mirror compared to a planar mirror of equal reflectivity. [ABSTRACT FROM AUTHOR]

We have investigated the influence of oriented microstructures at modified polyethylene terephthalate (PET) on the adhesion and alignment of Chinese hamster ovary (CHO) cells. For surface modification, the PET foils were exposed to the radiation of a laser-plasma extreme ultraviolet (EUV) source based on a double-stream gas-puff target. The emission of the plasma was focused onto the samples by means of a gold-plated ellipsoidal collector. The spectrum of the focused radiation covered the wavelength range from 9 to 70 nm. The PET samples were irradiated with the EUV pulses at a repetition rate of 10 Hz in a high vacuum. For control experiments, PET samples were also irradiated in air with the light of a 193 nm ArF-excimer laser. Different kinds of surface microstructures were obtained depending on the EUV or laser fluence and pulse number, including oriented wall- and ripple-type structures with lateral structure periods of a few µm. The surface morphology of polymer samples after the irradiation was investigated using a scanning electron microscope (SEM). Changes in chemical surface structure of the irradiated samples were investigated using X-ray photoelectron spectroscopy (XPS). We demonstrated that the cells show good adhesion and align along oriented wall- and ripple-type microstructures on PET surfaces produced by the EUV irradiation. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet (EUV) radiation is the electromagnetic radiation ranging from vacuum ultraviolet to soft X-rays. A single EUV photon carries enough energy to ionize any atom or molecule. The penetration depth of the radiation in any material is very short, ranging from tens to hundreds nanometers. Intense EUV pulses can remove material from the surface or modify its morphology or/and chemical structure. In this work, the radiation from a laser-plasma EUV source based on a double-stream gas-puff target was used for surface modification of polyethylene terephthalate (PET). The PET samples were irradiated with the EUV pulses emitted from krypton plasma and focused with a gold-plated ellipsoidal collector. The spectrum of the focused radiation covered the wavelength range from 9 to 70 nm. The PET samples were irradiated for 1 s–2 min at a 10-Hz repetition rate. Surface morphology of polymer samples after irradiation was investigated using a scanning electron microscope. Changes in chemical surface structure of the irradiated samples were investigated using an X-ray photoelectron spectroscopy. Different kinds of surface microstructures were obtained depending on the EUV fluence in a single pulse and the total EUV fluence. XPS measurements also revealed a modification of the chemical structure. [ABSTRACT FROM AUTHOR]

Surface modification of PMMA and FEP polymers using extreme ultraviolet (EUV) in two spectral ranges was investigated. A laser-plasma EUV source based on a double stream gas puff target equipped with an Au coated ellipsoidal collector was used for the experiment. The spectrum of the focused radiation from Kr plasma consisted of a narrow feature with a maximum at 10 nm and a long-wavelength tail up to 70 nm. Al and Zr filters were employed for the selection of radiation from these two spectral regions. The radiation fluences in the two cases were comparable. Polymer samples were mounted in the focal plane of the EUV collector and irradiated for 1–2 min with a 10 Hz repetition rate. Weak ablation accompanied by creation of micro- and nanostructures of different kinds was obtained in both cases. Significant differences in the surface structures after irradiation of PMMA and FEP in these two spectral regions were revealed. [ABSTRACT FROM AUTHOR]

Surface modification and micro-structuring of polymers for different application is mainly performed using ultraviolet (UV) radiation from excimer lamps or excimer lasers. In this case, however, the radiation penetration depth may exceed 100 μm, thereby degrading the polymer deep inside. On the other hand, extreme ultraviolet (EUV) radiation is absorbed in a layer approximately 100 nm thick only. In this work, the radiation from a laser-plasma EUV source based on a double-stream gas-puff target is focused with a gold-coated ellipsoidal collector for surface modification of polymethylmethacrylate (PMMA). The spectrum of the focused radiation consists of a narrow feature with maximum at 10 nm and a long-wavelength tail up to 70 nm. The PMMA samples are mounted in the focal plane of the EUV collector or at some distance downstream this plane and irradiated for 10–60 s with 10-Hz repetition rate. The irradiated polymer samples were investigated using a scanning electron microscope. When the EUV fluence exceeds 10 mJ/cm2, smooth ablation of PMMA was obtained. For lower fluences but close to this value, strong surface modifications appeared. [ABSTRACT FROM AUTHOR]

In this paper a possibility of performing fluorescence experiments in extreme ultraviolet (EUV) using a laboratory EUV source was demonstrated. Usually such measurements are performed using third-generation synchrotrons because of extremely low probability of fluorescence in this wavelength range. In this work a 10 Hz laser-plasma EUV source based on a gas puff target was used. Fluorescent radiation from Al and Si was registered. Despite relatively low spectral resolution, some differences in Si spectra coming from different kind of samples were revealed. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet (EUV) radiation is absorbed in a thin surface layer of any material. Irradiation of material samples with intense EUV pulses may cause different surface changes. Some of them, especially connected with material desorption, can be clearly visible using an optical or electron microscope. Other changes concerning crystal structure or chemical composition may not be visible under the microscope. They can however be detected using the EUV radiation itself. In this paper a new method of measurement of surface changes by irradiation with a laser-plasma EUV source is presented. The radiation was collected and focused on a material surface using a specially designed multifoil collector. Radiation scattered or excited in the material was detected with the use of a Wolter-type mirror coupled to a back-illuminated CCD camera. Depending on material samples, images with different intensity distributions were registered. For some samples, the intensity distributions of the images obtained before and after irradiation were slightly different. The intensity differences in such cases allowed us to obtain differential images. The appearance of such images was assumed to be evidence of surface changes. [ABSTRACT FROM AUTHOR]

The first results of experiments on direct photo-etching of heated PTFE using a 10 Hz X-ray source based on a laser-irradiated gas puff target are presented. X-ray radiation in the wavelength range from 6 to 20 nm was produced as a result of irradiation of a double-stream gas puff target with Nd:YAG laser pulses of energy 0.8 J and time duration 3 ns. The resulting X-ray pulses with energy of about 100–200 mJ were used to irradiate samples of PTFE to create microstructures by direct photo-etching. Strong enhancement of the photo-etching process was observed for samples heated up to 300 °C. [ABSTRACT FROM AUTHOR]

Abstract. X-ray emission from a double-stream gas puff target irradiated with a nanosecond Nd:glass laser pulse was studied for the first time. The target was formed by pulsed injection of a high-density gas into a gas cloud by using the double-nozzle setup. This new concept allows a high-density gaseous target to be formed at a relatively large distance from the nozzle output. Enhanced X-ray emission in the 1-keV energy range and a smaller source size were observed as compared to the ordinary gas puff target created by pulsed injection of gas into vacuum. This new approach should be useful in the development of a laser-produced X-ray source for various applications. [ABSTRACT FROM AUTHOR]

Abstract. We have measured low-energy ion emission from a gas-puff laser-plasma X-ray source. The ions may cause the degradation of the condenser mirror of the extreme ultra-violet projection lithography system. A 0.7 J in 8 ns Nd:YAG laser at 1.06 micro m was focused onto the xenon gaspuff target with an intensity of Is similar to 10[sup 12] W/cm[sup 2]. The silicon (111) plates, placed at a distance of 32mm from the laser-interaction region, were exposed with the xenon ions. The average ion energy was measured to be less than 50 eV with a Faraday-cup detector placed close to the silicon plates. The xenon deposition occurred in the silicon plates with a depth of less than 40nm. The deposition density was measured with a quadrupole secondary ion mass spectrometer to be 10[sup 21]/cm[sup 3] alter 1500 laser shots. The energy-conversion efficiency from the laser energy into the ions is 0.1%/4 pi sr/shot. For the lithography system, if we can remove such ion bombardment completely using novel techniques such as electro-magnetic devices or gas flow curtain techniques, the lifetime of the condenser mirror will be extended significantly. PACS: 52.25.Tx; 52.50.Jm; 52.75.Rx; 51.90.+r [ABSTRACT FROM AUTHOR]

Abstract. Measurements of X-ray emission in the wavelength range of 2-3 nm from a high-density nitrogen gas puff target irradiated with a nanosecond Nd:glass laser pulse were performed with an absolutely calibrated reflection grating spectrograph. The use of a gas puff target instead of a solid target eliminates the production of debris associated with solid targets, saving the high X-ray yield, compared to that obtained for solid targets. The laser-produced X-ray source based on a high-density nitrogen gas puff target could be employed in X-ray microscopy. [ABSTRACT FROM AUTHOR]

A desktop laser-plasma double-stream gas-puff target soft X-ray (SXR) source, operating in the so-called "water window" spectral range (λ = 2.3–4.4 nm). was successfully employed to acquire 3D tomographic images in transmission mode, using a Fresnel zone-plate microscope. The microscope, operating at the He-like nitrogen spectral line, 2.88-nm wavelength, allows acquiring 3D SXR volumetric reconstructions with a resolution of a few microns. The development of a compact system offers the possibility to obtain 3D reconstructed images in relatively short time and in a laboratory environment, without the involvement of large "photon facilities", such as synchrotrons or free electron lasers, however, with the modest volume resolution at this point. The possibility to obtain three-dimensional images in the SXR wavelength range using a compact, laser-plasma based system may be useful for material and life sciences, where it is required to visualize small features of the samples in 3D that are not visible with a single 2D image. Details about the equipment and the setup constructions as well as some imaged samples will be presented and discussed. [ABSTRACT FROM AUTHOR]