Laser Plasma Soft X-ray Source Research Articles

Nanometer-Resolution Imaging of Living Cells Using Soft X-ray Contact Microscopy

Soft X-ray microscopy is a powerful technique for imaging cells with nanometer resolution in their native state without chemical fixation, staining, or sectioning. The studies performed in several laboratories have demonstrated the potential of applying this technique for imaging the internal structures of intact cells. However, it is currently used mainly on synchrotrons with restricted access. Moreover, the operation of these instruments and the associated sample-preparation protocols require interdisciplinary and highly specialized personnel, limiting their wide application in practice. This is why soft X-ray microscopy is not commonly used in biological laboratories as an imaging tool. Thus, a laboratory-based and user-friendly soft X-ray contact microscope would facilitate the work of biologists. A compact, desk-top laboratory setup for soft X-ray contact microscopy (SXCM) based on a laser-plasma soft X-ray source, which can be used in any biological laboratory, together with several applications for biological imaging, are described. Moreover, the perspectives of the correlation of SXCM with other super-resolution imaging techniques based on the current literature are discussed.

Pulsed laser-plasma soft X-ray source as a compact tool for X-ray absorption spectroscopy of metal oxides

Laser-plasma short-wavelength source based on double-stream gas-puff target and emitting soft X-rays (SXR) is demonstrated as a compact tool suitable for X-ray absorption spectroscopy (XAS) of metal oxides. The source, optimized for emission in the spectral range between 1.5 and 5 nm from a krypton/helium target appears to be useful for the near edge X-ray absorption spectroscopy (NEXAFS) close to the Ti L-edge and Mo M-edge, as well as the K-edge of oxygen. High photon flux from the source enabled the simultaneous acquisition of the reference and transmission spectra using a flat-field grating spectrometer. The measurements conducted in the transmission mode revealed the spectral features near the absorption edges (Ti-L2,3 and Mo-M5) in metal oxides.

Chemical Dosimetry in the “Water Window”: Ferric Ions and Hydroxyl Radicals Produced by Intense Soft X Rays

A standard Fricke dosimeter was used to measure the absorbed dose via the oxidation yields of Fe3+ ions in an aqueous environment induced by soft X rays within the "water window" spectral range. We also exploited the property of a neutral solution containing terephthalic acid as a tool for selective detection of OH radicals. Both dosimetric systems were irradiated using the experimental pulsed laser-plasma soft X-ray source as well as conventional 1.25-MeV gamma rays. Radiation chemical yields of Fe3+ ions and OH radicals were determined to be (5.13 ± 0.94) × 10-1 µmol·J-1 (4.95 ± 0.91 100eV-1) and (2.33 ± 0.35) × 10-2 µmol·J-1 (0.23 ± 0.03 100eV-1), respectively. Measurements were supported by Monte Carlo simulations to estimate the linear energy transfer of the water window radiation. The simulation results are in good agreement with expected linear energy transfer of ions inducing the same Fe3+ ion and OH radical radiation chemical yield.

EXAFS of titanium LIII edge using a compact laboratory system based on a laser-plasma soft X-ray source

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.

NEXAFS at nitrogen K-edge and titanium L-edge using a laser-plasma soft x-ray source based on a double-stream gas puff target

We present a possibility of reaching higher energy absorption edges of organic materials, beyond the carbon K-edge, in the near edge X-ray absorption fine structure (NEXAFS) spectroscopy technique using a compact laser-produced plasma soft X-ray (SXR) source based on a double-stream gas puff target. The source was optimized for emission in the SXR spectral range from 1.5 to 5 nm wavelength using the krypton/helium target. The emission spectrum of the source and the absorption spectrum of the investigated sample were measured simultaneously by means of a grazing incidence spectrometer, equipped with a single, large aperture diffractive element. Based on both spectra, the optical density was computed for the silicon nitride membranes in a transmission mode, to reveal the NEXAFS features near the nitrogen K-edge. Moreover, due to spectral narrowing of the SXR emission by the use of titanium filter, reaching the titanium L-edge was also possible. Multiple SXR pulse data were compared to single SXR pulse (single-shot) data as well as to the numerical simulations. In this paper, the detailed information about the source, spectroscopy system, and the results of NEXAFS measurements is presented and discussed.

Optical coherence tomography (OCT) with 2\u2009nm axial resolution using a compact laser plasma soft X-ray source

We present optical coherence tomography (OCT) with 2 nm axial resolution using broadband soft X-ray radiation (SXR) from a compact laser plasma light source. The laser plasma was formed by the interaction of nanosecond laser pulses with a gaseous target in a double stream gas puff target approach. The source was optimized for efficient SXR emission from the krypton/helium gas puff target in the 2 to 5 nm spectral range, encompassing the entire “water-window” spectral range from 2.3 nm to 4.4 nm wavelength. The coherence parameters of the SXR radiation allowed for the OCT measurements of a bulk multilayer structure with 10 nm period and 40% bottom layer thickness to period ratio, with an axial resolution of about 2 nm and detect multilayer interfaces up to a depth of about 100 nm. The experimental data are in agreement with OCT simulations performed on ideal multilayer structure. In the paper, detailed information about the source, its optimization, the optical system, OCT measurements and the results are presented and discussed.

Efficient soft x-ray sources from laser-irradiated gold foam targets with well-controlled impurities

As an important x-ray source, enhancement of x-ray emissions from laser-produced plasmas is significant for various applications. Due to less expanding kinetic loss, gold foam with low initial density can have an enhanced x-ray conversion efficiency compared with solid-density gold. However, low-Z impurities within gold foam targets will diminish the enhancement remarkably, and should be tightly controlled. This paper presents an experimental study of a high brightness laser plasma soft x-ray source, based on a g gold foam target with negligible impurities irradiated by nanosecond laser pulses with power density around 3 × 10 W at the Shenguang II laser facility. A conversion efficiency, from multi-eV to multi-keV, of % is achieved in the x-ray emissions—about 21% relative enhancement compared with a solid-density gold target, and the highest conversion efficiency for Au foam planar targets yet. Good agreement has been achieved between the semi-analytical model prediction and the experimental results.

Development and characterization of a laser-plasma soft X-ray source for contact microscopy

Abstract In this work, we present a compact laser-produced plasma source of X-rays, developed and characterized for application in soft X-ray contact microscopy (SXCM). The source is based on a double stream gas puff target, irradiated with a commercially available Nd:YAG laser, delivering pulses with energy up to 740 mJ and 4 ns pulse duration at 10 Hz repetition rate. The target is formed by pulsed injection of a stream of high-Z gas (argon) into a cloud of low Z-gas (helium) by using an electromagnetic valve with a double nozzle setup. The source is designed to irradiate specimens, both in vacuum and in helium atmosphere with nanosecond pulses of soft X-rays in the “water-window” spectral range. The source is capable of delivering a photon fluence of about 1.09 × 10 3 photon/μm 2 /pulse at a sample placed in vacuum at a distance of about 20 mm downstream the source. It can also deliver a photon fluence of about 9.31 × 10 2 photons/µm 2 /pulse at a sample placed in a helium atmosphere at the same position. The source design and results of the characterization measurements as well as the optimization of the source are presented and discussed. The source was successfully applied in the preliminary experiments on soft X-ray contact microscopy and images of microstructures and biological specimens with ∼80 nm half-pitch spatial resolution, obtained in helium atmosphere, are presented.

クライオターゲットによる「水の窓」レーザ生成プラズマ軟X線源

クライオターゲットによる「水の窓」レーザ生成プラズマ軟X線源

Recent advancements in the “water-window” microscopy with laser-plasma SXR source based on a double stream gas-puff target

AbstractAn overview of our recent developments, regarding “water-window” soft X-ray (SXR) microscopy based on a laser-plasma double stream gas puff target sources is presented. The work, presented herein, describes two approaches to SXR microscopy. The first one is a low spatial resolution, achromatic SXR microscopy, employing Wolter type-I objective. The second one is a nanometer spatial resolution SXR microscopy, with the use of a Fresnel zone plate objective, for imaging various objects with quasimonochromatic light, emitted from a double stream gas puff target based short wavelength source. The developments regarding both systems are presented, as well as the possible applications, for which the SXR microscope was already employed. Such compact, table-top size, laboratory type microscopy setups may be employed in the near future for complementary-like studies to other, often used, microscopy techniques.

Stability of liquid-nitrogen-jet laser-plasma targets

Microscopic jets of cryogenic substances such as liquid nitrogen are important regenerative high-density targets for high-repetition rate, high-brightness laser-plasma soft x-ray sources. When operated in vacuum such liquid jets exhibit several non-classical instabilities that negatively influence the x-ray source's spatial and temporal stability, yield, and brightness, parameters that all are important for applications such as water-window microscopy. In the present paper, we investigate liquid-nitrogen jets with a flash-illumination imaging system that allows for a quantitative stability analysis with high spatial and temporal resolution. Direct and indirect consequences of evaporation are identified as the key reasons for the observed instabilities. Operating the jets in an approximately 100 mbar ambient atmosphere counteracts the effects of evaporation and produces highly stable liquid nitrogen jets. For operation in vacuum, which is necessary for the laser plasmas, we improve the stability by introducing an external radiative heating element. The method significantly extends the distance from the nozzle that can be used for liquid-jet laser plasmas, which is of importance for high-average-power applications. Finally, we show that laser-plasma operation with the heating-element-stabilized jet shows improved short-term and long-term temporal stability in its water-window x-ray emission.

Extreme ultraviolet and soft X-ray imaging using compact laser-plasma sources based on a double stream gas-puff target

New developments in science and technology require imaging tools and techniques capable of imaging with increased contrast and high spatial resolution, such as an extreme ultraviolet (EUV) and soft X-ray (SXR) microscopy. In this paper, we report on our recent activities related to various imaging techniques in the EUV and SXR region of electromagnetic spectrum, employing a double stream gas-puff target source. Those techniques has been successfully used for studies of morphology of thin silicon membranes coated with NaCl crystals, samples composed of ZnO nanofibers and biological samples. Full Text: PDF References D. Attwood, Soft X-Rays and Extreme Ultraviolet Radiation, Cambridge University, Cambridge, England, 1999. CrossRef W. Chao, J. Kim, S. Rekawa, P. Fischer and E. H. Anderson, "Demonstration of 12 nm Resolution Fresnel Zone Plate Lens based Soft X-ray Microscopy", Opt. Express 17, 20, 17669 (2009) CrossRef G. Vaschenko, et al., "Sub- 38nm resolution tabletop microscopy with 13nm wavelength laser light", Opt.Lett. 31, 1214?1216 (2006) CrossRef C. A. Brewer, et al., "Single-shot extreme ultraviolet laser imaging of nanostructures with wavelength resolution", Opt. Lett. 33, 5, 518, (2008) CrossRef K. W. Kim, et al., "Compact soft x-ray transmission microscopy with sub-50 nm spatial resolution", Phys. Med. Biol. 51, N99-N107 (2006) CrossRef L. Juschkin, R. Freiberger, and K. Bergman, "EUV microscopy for defect inspection by dark-field mapping and zone plate zooming", J. Phys.: Conf. Ser. 186, 012030 (2009) CrossRef P. W. Wachulak, A. Bartnik and H. Fiedorowicz, "Sub-70 nm resolution tabletop microscopy at 13.8 nm using a compact laser?plasma EUV source", Opt. Lett. 35, 14, 2337-2339 (2010) CrossRef P. W. Wachulak, A. Bartnik, H. Fiedorowicz, and J. Kostecki, "A 50nm spatial resolution EUV imaging?resolution dependence on object thickness and illumination bandwidth", Opt. Exp. 19, 10, 9541?9550 (2011) CrossRef P. W. Wachulak, et al., "A compact, quasi-monochromatic laser-plasma EUV source based on a double-stream gas-puff target at 13.8 nm wavelength", Applied Physics B 100, 3, 461-469, (2010) CrossRef R. L. Kelly, Journal of Physical and Chemical Reference Data, 16, supplement 1 (1987) DirectLink The ZP was fabricated by Zone Plates Ltd., using electron beam lithography in 220nm thick PMMA (polymethyl methacrylate) layer spin- coated on top of a 50nm thick silicon nitride Si3N4 membrane. P. W. Wachulak, A. Bartnik, H. Fiedorowicz, D. Panek, P. Bruza, "Imaging of nanostructures with sub-100 nm spatial resolution using a desktop EUV microscope", Appl. Phys. B 109, 105-111 (2012) CrossRef P.W. Wachulak, et al., "Study of crystalline thin films and nanofibers by means of the laser?plasma EUV-source based microscopy", Radiation Physics and Chemistry 93, 54-58 (2013) CrossRef L.B. Da Silva, et al., "X-ray laser microscopy of rat sperm nuclei", Science 258, 269 (1992) CrossRef P. W. Wachulak, et al., "Water-window microscopy using a compact, laser-plasma SXR source based on a double-stream gas-puff target", Appl. Phys. B 111, 2, 239-247 (2013) CrossRef P. W. Wachulak, et al., "Sub 1-?m resolution ?water-window? microscopy using a compact, laser-plasma SXR source based on a double stream gas-puff target", Nucl. Instr. and Meth. B 311, 42-46(2013) CrossRef H. Wolter, "Verallgemeinerte Schwarzschildsche Spiegelsysteme streifender Reflexion als Optiken für Röntgenstrahlen", Ann. Physik 10, 286 (1952) CrossRef

In situ observation of cellular organelles with a contact x-ray microscope

A contact x-ray microscope coupled with a highly intense laser plasma soft x-ray source has been developed and in situ observations of cellular organelles have been conducted. The soft x-rays were generated by irradiating a high power laser pulse onto a thin-foiled gold target and about 1.3×1015 photons/sr were obtained, which allowed the inner structures of live wet biological cells to be imaged. Single shot flash imaging is a key technique to image cellular organelles of live biological cells avoiding degradation of the spatial resolution of the images resulting from motion blur and radiation damage. The use of a fluorescence microscope to identify cellular organelles in conjunction with the soft x-ray microscope has allowed several cellular organelles to be identified precisely in the soft x-ray images. Combining the fluorescence microscope with the soft x-ray microscope will be very useful and will establish the technique as a powerful tool to analyze living function of biological cells.

“Water window” compact, table-top laser plasma soft X-ray sources based on a gas puff target

Abstract We have developed compact, high repetition, table-top soft-X-ray sources, based on a gas puff target, emitting in “water window” spectral range at λ = 2.88 nm from nitrogen gas target or, in 2–4 nm range of wavelengths, from argon gas target. Double stream gas puff target was pumped optically by commercial Nd:YAG laser, energy 0.74 J, pulse time duration 4 ns. Spatial distribution of laser-produced plasma was imaged using a pinhole camera. Using transmission grating spectrometer, argon and nitrogen emission spectra were obtained, showing strong emission in the “water window” spectral range. Using AXUV100 detector the flux measurements of the soft-X-ray pulses were carried out and are presented. These debris free sources are table-top alternative for free electron lasers and synchrotron installations. They can be successfully employed in microscopy, spectroscopy and metrology experiments among others.

Excimer-Laser-Driven EUV Plasma Source for Single-Shot Projection Lithography

We present a low-cost microexposure tool for projection lithography at 14.4 nm we have designed and operated at the ENEA Research Centre, Frascati. It is a laboratory-scale system based on a Schwarzschild-type projection optics which uses a laser-plasma soft X-ray source, equipped with a patented debris mitigation system in order to preserve the collector optics. As a preliminary result, we achieved a 90-nm optical resolution patterning on commercial resist. A sharp improvement in resolution size is expected when operating this tool by a large-output energy excimer laser in order to obtain a single-shot patterning.

X‐ray microscopy of plant cells by using LiF crystal as a detector

A lithium fluoride (LiF) crystal has been utilized as a new soft X-ray detector to image different biological samples at a high spatial resolution. This new type of image detector for X-ray microscopy has many interesting properties: high resolution (nanometer scale), permanent storage of images, the ability to clear the image and reuse the LiF crystal, and high contrast with greater dynamic range. Cells of the unicellular green algae Chlamydomonas dysosmos and Chlorella sorokiniana, and pollen grains of Olea europea have been used as biological materials for imaging. The biological samples were imaged on LiF crystals by using the soft X-ray contact microscopy and contact micro-radiography techniques. The laser plasma soft X-ray source was generated using a Nd:YAG/Glass laser focused on a solid target. The X-ray energy range for image acquisition was in the water-window spectral range for single shot contact microscopy of very thin biological samples (single cells) and around 1 keV for multishots microradiography. The main aim of this article is to highlight the possibility of using a LiF crystal as a detector for the biological imaging using soft X-ray radiation and to demonstrate its ability to visualize the microstructure within living cells.

レーザと電子ビームによる軟X線，ガンマ線光源の研究

Soft x-ray and gamma-ray beam sources are developed by using laser and high energy electron beams. Laser plasma soft x-ray source is a cryogenic Xe target irradiated by a high average power (>100 W) and high peak power (30MW, 0.3 J/10 ns) laser. A conversion efficiency from the laser energy to the soft x-ray (70-200eV) energy of 22% was achieved. Laser Compton gamma-ray source on a synchrotron radiation facility, NewSUBARU, is new quasi-monochromatic high energy photon beam. World highest class gamma-ray flux of more than 106 photons/s is generated at photon energy range of 6 to 17 MeV.

Quantitative analysis of thin samples by differential absorption imaging using a laser-plasma soft X-ray source

We consider the application of the differential absorption imaging technique in the soft X-ray region. The surface-density maps of test samples containing bromine, resulting from the application of the differential absorption imaging technique, are presented. Images of the samples were obtained in an X-ray monochromatic projection imaging scheme based on a spherically bent crystal using line emission close to the $L_2$ edge of bromine from a microplasma produced by focusing a nanosecond laser on the surface of an aluminum target.

Differential absorption imaging for elemental analysis of thin samples using a soft laser-plasma X-ray source

The differential X-ray imaging technique is a powerful tool for the detection of small concentrations of contrast agents in samples, as demonstrated recently by many biological and medical applications using synchrotron radiation. In this paper, we present an implementation of this technique using a laser-plasma soft X-ray source combined with an X-ray imaging system based upon a spherically bent Bragg crystal. Using a test sample containing a solution of LiBr of known concentration, we demonstrate that the use of our table-top configuration is suitable to detect Br inside our sample via differential imaging at the L 2 edge of Br at 7.7684 Å .

Soft laser-plasma X-ray source for differential absorption imaging of tracing elements in thin samples

The differential imaging technique is particularly suitable for the detection of small concentrations of contrasts agents for biological and medical applications in samples using X-ray radiography. In this paper, we present an application of this technique using a laser-plasma soft X-ray source combined with a bent crystal. Using a Fresnel plate as a test object, we were able to obtain spatial resolutions of the order of a few tens of microns. The use of our configuration to perform differential imaging of a test-sample at the L2 edge of Br at 1,596 eV is finally demonstrated.