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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., (2008 Wiley-Liss, Inc.)

In this article, a method to reveal the presence of Mg content inside the different parts of leaves of Hedera helix is presented. In fact a sample of a Hedera helix's leaf, commonly characterized by a green and a white side, is analyzed under X-ray radiation. The presence of two zones with different colors in the Hedera helix's leaf has not been explained. In this connection, there are presently three hypotheses to explain the characteristic double-color appearance of the leaf. The first hypothesis suggests a different cytoplasmic inheritance of chloroplasts at the cell division, the second a different allelic composition, homozygote and heterozygote, between the two zones, and finally the third the action of a virus which changes the color properties in the Hedera's leaves. The resulting effect is a different content of "something" between the green and the white side. We utilized X-ray radiation, obtained from a plasma source with a Mg target, to image Hedera helix leaves and we found that the green side of the leaf is highlighted. We may suppose that the reason why the X-rays from a Mg plasma source, allow us to pick up the green side is probably due to the greater presence of the amount of Mg (from chlorophyll or other complexes and/or salts) in the two sides, green and white, of the leaf., ((c) 2008 Wiley-Liss, Inc.)

High contrast imaging of in vivo Chlorella sorokiniana cells with submicron spatial resolution was obtained with a contact water window X-ray microscopy technique using a point-like, laser-plasma produced, water-window X-ray radiation source, and LiF crystals as detectors. This novel type of X-ray imaging detectors is based on photoluminescence of stable electronic point defects, characterized by high intrinsic resolution. The fluorescence images obtained on LiF crystals exposed in single-shot experiments demonstrate the high sensitivity and dynamic range of this new detector. The powerful performances of LiF crystals allowed us to detect the exudates of Chlorella cells in their living medium and their spatial distribution in situ, without any special sample preparation., (2007 Wiley-Liss, Inc)

A method for detecting cadmium uptake in leaves of Saponaria officinalis doped with a solution of cadmium acetate is described. The technique based on the exposure of dried leaves to X-rays of a wavelength close to that of the metal K-edge could be useful for phytoremediation studies as it could reveal the bioaccumulation in plants due to the treatment either in vivo or in vitro with heavy metals. X-ray microradiography measurements are in agreement with those from peroxidase enzyme assay utilized to follow the oxidative damage induced by heavy metals. At present, as we will see in this report, microradiography has still poorer sensitivity in comparison with enzyme assay, but it has the advantage of being faster, not destructive, and usable even at very high doping levels, where the enzyme assay technique results are fully saturated. Further analysis of the optical density values could lead to a quantitative measurement of the heavy metal in the sample. Thus, the technology developed in this article could be useful for tracing the intake in phytoremediation studies., (Copyright 2004 Wiley-Liss, Inc.)

We present a review on the use of X-ray detectors based on lithium fluoride crystals both for the determination of the parameters of the X-ray sources and for the recording of radiographic images obtained with them. The results are presented for experiments on a radiographic analysis of biological objects and inorganic structures based on an image obtained from the thermal radiation of a high-temperature laser-plasma source, coherent X-ray radiation of a plasma laser, and a free-electron laser, as well as the generation of higher harmonics of the optical laser radiation. [ABSTRACT FROM AUTHOR]

The response of lithium fluoride (LiF) crystal detectors to monochromatic X-rays is measured in the multi-kilo-electron-volt range. This response, as a function of the X-ray dose, is independent of photon energy with no saturation level found. The response, as a function of the incident energy flux, is found to increase for photons of lower energy due to the differing attenuation lengths of X-ray photons within the crystal. Small differences are seen between different confocal microscopes used to scan the data, suggesting the need for absolute calibration. The spatial resolution of the LiF is also measured (1.19–1.36 μm) and is found to be independent of incident photon energy. Finally, a photometric study is performed in order to assess the feasibility of using these detectors at current X-ray free electron laser and laser facilities worldwide. [ABSTRACT FROM AUTHOR]

The emission of X-rays from solid tin targets irradiated by low-energy (few mJ) femtosecond laser pulses propagated through air plasma sparks is investigated. The aim is that to better understand the X-ray emission mechanism and to show the possibility to produce proper radiation for spectroscopic and imaging applications with a table-top laser system. The utilization of a controlled ultrashort prepulse is found necessary to optimize the conversion efficiency of laser energy into Lα radiation. The optimum contrast between the main pulse and the controlled prepulse is found about 102. A correlation between the laser contrast value and the laser near-infrared spectra at the exit of the plasma spark is observed. [ABSTRACT FROM PUBLISHER]

Spatial structures of ablative mass flow produced by femtosecond laser pulses are studied. In experiments with a gold film, the Ti:sapp laser pulse having a focal size of 100 microns on a target was used, while a soft X-ray probe pulse was utilized for diagnostics. The experimental data are compared with simulated mass flows obtained by two-temperature hydrodynamics and molecular dynamics methods. Simulation shows evolution of a thin surface layer pressurized after electron-ion thermalization, which leads to melting, cavitation and formation of spallation liquid layer. The calculated asymptotic surface velocity of this layer as a function of fluence is in reasonably good agreement with experimental data. [ABSTRACT FROM AUTHOR]

An improved high luminosity, easily spectrally tunable backlighting scheme based on a spherically bent crystal is considered in this paper. Contrary to the traditional backlighting scheme, we used crystal far from normal incidence, and the backlighter source was inside the Rowland circle. With the presented configuration, we obtained a spatial resolution up to 8 mm in the desired direction with an X-ray backlighting energy close to 5 keV. Detailed discussions and ray-tracing calculations show that with this convenient scheme resolution down to 5 mm can be achieved. A dedicated application to high energy density physics is presented: the radiography of shock compressed matter. [ABSTRACT FROM AUTHOR]

In this work, we report a method to observe soft X-ray radiographs at nanoscale of various kind of samples, biological and metallic, stored in a thin layer of lithium fluoride, employing scanning near-field optical microscopy with an optical resolution that reaches 50 nm. lithium fluoride material works as a novel image detector for X-ray nano-radiographs, due to the fact that extreme ultraviolet radiation and soft X-rays efficiently produce stable point defects emitting optically stimulated visible luminescence in a thin surface layer. The bi-dimensional distribution of the so-created defects depends on the local nanostructure of the investigated sample. [ABSTRACT FROM AUTHOR]

Radiation emission of silicon and aluminum plasmas produced by 40-ps laser pulses with peak intensity above 1014 W/cm2 was studied. High-resolution soft X-rayspectra of H-like and He-like ions were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the intercombination lines of He-like ions with the results of model calculations. Such comparisons gave average values of the electron number density Ne=(1-1.9)×1021 cm-3 and the electron temperature Te=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. The plasma size is about 100 μm. According to our estimations, more than 1012 photons were produced within the resonance line spectral width and in the solid angle 2π during the total decay period. [ABSTRACT FROM AUTHOR]

The use of lithium fluoride (LiF) crystals and films as imaging detectors for EUV and soft-x-ray radiation is discussed. The EUV or soft-x-ray radiation can generate stable color centers, emitting in the visible spectral range an intense fluorescence from the exposed areas. The high dynamic response of the material to the received dose and the atomic scale of the color centers make this detector extremely interesting for imaging at a spatial resolution which can be much smaller than the light wavelength. Experimental results of contact microscopy imaging of test meshes demonstrate a resolution of the order of 400 nm. This high spatial resolution has been obtained in a wide field of view, up to several mm2. Images obtained on different biological samples, as well as an investigation of a soft x-ray laser beam are presented. The behavior of the generated color centers density as a function of the deposited x-ray dose and the advantages of this new diagnostic technique for both coherent and noncoherent EUV sources, compared with CCDs detectors, photographic films, and photoresists are discussed. [ABSTRACT FROM AUTHOR]

This paper reports on dual energy micro-radiography and tomography techniques applied both to thin plant leaves treated with copper or lead solutions and on Cu-treated small roots and stem sections, performed at the SYRMEP X-ray beamline of ELETTRA synchrotron facility in Trieste (Italy). The features of the source allowed us to apply different imaging techniques with an extremely vast field of view, up to 160 ×6 mm2 and 28×6 mm2 for micro-radiography and tomography experiments, respectively. The feasibility of getting positive indications on metal accumulation in leaves, sections of roots and stems, stem and root whole cylindrical pieces has been checked. [ABSTRACT FROM AUTHOR]

The characterization of the laser beam intensity distribution of a highly saturated 46.9-nm soft X-ray laser excited by capillary discharges is reported. The laser produces a total output energy of 300 μJ/pulse by amplification in plasma channels having lengths up to 0.45 m. A regime of laser amplification, which is almost free from the effect of the refraction defocusing, is experimentally determined. This regime produces a soft X-ray laser beam with an intense sub­milliradiant component. In the longer active medium the laser intensity distribution reaches the divergence of 0.6 mrad, which approaches the limit of diffraction. A comparison of the experimental results with the simulations performed with a ray-tracing code shows that the small divergence of the beam could be attributed to the effect of a weak index waveguiding of the laser beam through the long plasma channels. [ABSTRACT FROM AUTHOR]

The X-ray lines of ions in a solid target interacting with picosecond laser pulses of moderate intensity (2 × 10[sup 17] W/cm[sup 2]) were measured on the “Neodim” laser facility. X-ray Ly[sub α] emission spectra of hydrogen-like fluorine ions were observed. Satellite lines were also observed, evidencing the presence of intense plasma oscillations. The positions and separation between the satellites allow their assignment to the intense electrostatic oscillations with an amplitude larger than 10[sup 8] V/cm and a frequency of about 7 × 10[sup 14]s[sup –1] that is noticeably lower than the laser frequency ω[sub las] ∼ 1.8 × 10[sup 15] s[sup –1]. It is suggested that these oscillations may be due to strong plasma turbulence caused by the development of plasma oscillations of the Bernstein-mode type under the action of a strong magnetic field generated in plasma. The experimental results are compared with the calculated spectra of multicharged ions. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Variation of the velocity of Ca[sup 6+] ions with initial energies of 5.9 and 11.4 MeV/nucleon has been experimentally studied in the course of ion stopping in a solid aerogel target. The method is based on measuring the Doppler shift in the K-shell spectrum of decelerated Ca[sup 19+] and Ca[sup 18+] ions. High spatial resolution (30–50 μm) in the direction of the ion beam propagation achieved simultaneously with high spectral resolution (λ/Δλ = 1000–3000) in the X-ray wavelength interval of 2–4 Å allowed the ion beam dynamics in the solid target to be directly measured. By measuring variations in the relative intensity of spectral lines, it is possible to monitor the redistribution of the ions over charged states during their motion in the target. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

We report the attempt to prepare free-standing spherically bent Si crystals with radii of curvature as small as 30 cm and large uniform working areas up to several cm². We also report on the use of these crystals in the Laue geometry to record two-dimensional high spatial resolution x-ray images in the hard x-ray region (λ∼0.5 Å). We discuss how these bent crystals were made, and show how these spherically bent crystals were used in the Laue geometry to obtain hard x-ray images of test objects at the silver K-alpha wavelength at two different magnifications. The mean spatial resolution of this x-ray imaging scheme, determined from the recorded image traces, was found to be better than 10 µm over a field of view of 1.5×1.5 mm. Contributions of possible focusing mechanisms (dynamical and polychromatic) are discussed. Additional theoretical understanding of how such a scheme is working is needed. [ABSTRACT FROM AUTHOR]

The x-ray spectra of a plasma produced by heating CO[sub 2] clusters with intense femtosecond laser pulses with λ = 0.8 µm and λ = 0.4 µm are investigated. Spatially resolved x-ray spectra of the cluster plasma are obtained. The observed characteristic features of the x-ray emission spectra show unequivocally that such a plasma contains quite a large relative number of ions (...10[sup -]2 - 10[sup -3]) with energies of 0.1-1 MeV. The contour of the O VIII Ly[sub α] line is found to have characteristic features that are especially conspicuous when the clusters are heated with second-harmonic pulses. These features cannot be explained by any mechanisms known to the authors. [ABSTRACT FROM AUTHOR]

Describes monochromatic x-ray backlighting, a diagnostic method for dense plasmas. Principle of monochromatic x-ray backlighting; Mica crystals; Shadow image of a test object with maximum spatial resolution using radiation with different wavelengths; Ability of the mica crystals to reflect radiation in many orders of reflection.

The intense soft x-ray light source using the supersonic expansion of the mixed gas of He and CO2, when irradiated by a femtosecond Ti:sapphire laser pulse, is observed to enhance the radiation of soft x-rays from the CO2 clusters. Using this soft x-ray emissions, nanostructure images of 100-nm-thick Mo foils in a wide field of view (mm2 scale) with high spatial resolution (800 nm) are obtained with high dynamic range LiF crystal detectors. The local inhomogeneities of soft x-ray absorption by the nanometer-thick foils is measured with an accuracy of less than ±3%. [ABSTRACT FROM AUTHOR]

Profiles of nanometric aluminum and parylene foils have been characterized by soft x-ray contact imaging using a laser-plasma source and a LiF crystal as detector. Due to the characteristic emission of this source in a 2π angle, it was possible to obtain the sample image in a wider field of view with respect to coherent sources. LiF crystal is a cheap and robust imaging detector for soft x-ray radiation, that allows one to get high spatial resolution images of thin films with thickness from hundreds down to a few tens of nanometers. [ABSTRACT FROM AUTHOR]

We demonstrate a new high-order harmonic generation mechanism reaching the "water window" spectral region in experiments with multiterawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving &mgr;J/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

Abstract: Among insulating materials containing point defects, lithium fluoride (LiF) is a radiation-sensitive alkali halide well known in dosimetry and as active medium in light-emitting devices and lasers. Electronic point defects can be produced in LiF crystals and films by different kinds of radiation. Some of these electronic defects, known as colour centres, are optically active, with broad absorption and emission bands in the visible spectral range. Novel thin-film imaging detectors for extreme ultraviolet and soft X-rays, based on photoluminescence from aggregated colour centres in LiF, have been proposed and are currently under development, successfully extending their operation also in the hard X-ray region, up to 10keV. Among the main peculiarities of LiF-based detectors, there are intrinsic high spatial resolution, in principle limited only by the point defect size, large field of view and wide dynamic range. These imaging detectors feature great versatility, as they can be grown in the form of thin films on different substrates by well-assessed physical deposition techniques. We present the promising results obtained using different X-ray laser–plasma sources in the field of nanotechnology, biology and in material science in view of future perspectives of research and development. [ABSTRACT FROM AUTHOR]

We report a substantial improvement of the output characteristics of a capillary discharge single-pass 46.9 nm Ne-like Ar soft-X-ray laser obtained by increasing the length of laser amplifier from 20 up to 45 cm. The longest plasma amplifier is characterized by an aspect ratio well exceeding 1000:1. The plasma columns are pumped by long 180 ns half-cycle duration, low amplitude 17–20 kA current pulses inside 3 mm in diameter alumina capillary channels filled with Ar at pressures of 0.25–0.55 Torr. Through the elongation of the plasma we produce a highly saturated regime of operation, where the plasma medium is three times the saturation length, the output pulse energy is of 300 μJ and the pulse duration of 1.7 ns. The far-field intensity distribution, reaching value <1 mrad and the coherence properties of the laser, both have been also shown to improve with the increase of the capillary length. The stable operation of the laser has been produced at pulse repetition rate up to 0.1 Hz. [Copyright &y& Elsevier]