Pinching capillary discharge in nitrogen is investigated for the purpose of development of laser recombination pumping. An apparatus, previously realized for argon capillary laser pumping, was used to understand details of pinching mechanism and emission characteristics for capillary filled by nitrogen. Time dependences of radiation intensities emitted in the wavelength range 1.9 - 2.5 nm and time integrated in the spectral range 10 - 20 nm were measured under various pressures. A computer model is used to describe the pinch dynamics and to estimate the radiation characteristics. EUV reflection grating spectrometer coupled to BI CCD camera and filtered PIN diode were used for time integrated and time resolved spectral measurements respectively. The measured profiles of radiation intensities are compared with the computer simulations of time dependences of selected energy level populations that correspond to the hydrogen- and helium- like ion line emission in the detected spectral range. Complex method for spectral image restoration was developed.
New approaches of a spectrally tunable backlighting schemes based on a spherically bent crystal are considered. In a contrary to the traditional backlighting scheme, in which the investigated objects should be placed between the backlighter and the crystal, for the considered schemes an object is placed downstream of the crystal, before the tangential or after the sagittal focus and an image of the object is recorded at the distance from the object corresponded to the needed magnification. The magnification is defined by the ratio of the distances form the sagittal focus to the detector and from the object to the sagittal focus. A ray tracing modeling and experimental images of test meshes, obtained at an incidence angles of the backlighter radiation of 10° and 22°, are presented. It is demonstrated that, at incident angles up to 22°, a linear transformation of the obtained astigmatic images allows to reconstruct them with an accuracy (5 - 15%). A spatial resolution around 10 μm in a field of view of some mm2 is achieved, for the spectral range around 9 Å. It is also demonstrated that spherically bent crystals could be used for X-ray imaging of a self emitting plasma structures with a spatial resolution at least 50 μm in a field of view of some square millimeters for angles of incidence up to 22°.
A new imaging detector for EUV or soft-X-ray radiation based on optically stimulated luminescence (OSL) of lithium fluoride (LiF) films or crystals is presented. The first micro-radiography images of biological samples and of meshes obtained on LiF using a laser-plasma source or an X-ray laser are shown, and (up to now) a resolution better than one micron is demonstrated. The dependence of the coloration density vs the deposited X-ray dose is considered and the advantages of this new diagnostic technique for both coherent and non-coherent EUV sources, compared with CCDs detectors, photographic films and photoresists are discussed. This new detector is extremely suitable for laser plasmas and for X-ray lasers sources.
The recent progress in the development of the tabletop soft x-ray lasers pumped by capillary discharges has opened the possibility of the widespread use of these coherent sources for applications. In this paper, we present the latest results achieved in our laboratory concerning the optimization of a 46.9nm capillary discharge pumped soft x-ray laser and the imaging of the laser beam on Lithium Fluoride (LiF, films), which appears to be a new promising x-ray detector. The use of LiF allows a high spatial resolution (smaller than 1μm) on large areas, high-contrast imaging and simple manipulation. The laser, which is pumped by 18-20kA, 150-180ns long current pulses at a repetition rate of 0.1Hz, is produced in 3.2mm diameter up to 45cm length alumina capillary tubes filled with Ar at the initial gas pressure of 300-600mTorr. At the capillary lengths examined, the laser is operating in the saturation regime giving an output energy of about 300μJ per pulse and high coherence degree.
The effect of the transverse-direction electrical fields on the stability and dynamics of a capillary discharge Z-pinch, at conditions for which soft x-ray lasing in Ne-like Ar has been demonstrated, is studied. It is shown that the transverse electrical fields of the sliding surface discharge provide the instability-free compression and heating of the plasma. The stable and homogeneous heating and compression allows achievement of the appropriate conditions for the soft x-ray lasing in Ne-like Ar. Numerical calculations using the MHD model of the discharge yield new predictions for dynamics and stability of the plasma collapse in the presence of the transverse electrical fields and explain details of experimental observations without artificial adjustments.
A novel experimental setup for transmission x-ray microscopy is presented. It is based on the use of a point isotropic x- ray source and a single spherical crystal. The x-ray beam intensity is modulated by the object attenuation, then monochromatized and enlarged using a spherical crystal and, lastly, imaged using a detector downstream of the crystal. We demonstrate by ray tracing technique and experimental testing that this system allows microscopy studies with image resolution better than the dimensions of the source, high magnification ratios, and great field of view. Microscopes using this model ca be easily built using different micro x-ray sources, like conventional x-ray tube generators, x-rays emitted by laser generated plasmas or synchrotron radiation. Utilization of spherically bent crystals to obtain high-resolution, large field, monochromatic images in a wide range of Bragg angles is demonstrated for the first time. High quality monochromatic images with high magnification about 15-35 times and spatial resolution over a large field of view were obtained. Some possible applications and preliminary experimental verification of the feasibility of the setup are also presented.
We report on a fast soft x-ray source consisting in a high temperature small diameter plasma column produced by electric discharge in a ceramic capillary. This source was developed to produce pulses of few hundred nanosecond duration for EUV lithography, x-ray microscopy applications and also with the aim of developing a soft x-ray amplifier. We obtained experimental results concerning the intensity and spectral analysis of the emitted x radiation pumped by a 30-40 kA, 100-200 ns, electric discharge at 1 Torr pressure in Ar gas. We refer also on the spectra obtained using CO2, as plasma medium, after the optimization of the discharge setup and electrical parameters.
Propagation of the soft x-rays, which have been generated by a small-diameter incoherent source, through the straight and tapered plane capillaries is studied using the Fresnel- Kirchhoff diffraction theory. The diffraction and interference are manifested by appearance of the diffraction fringes in the far-field zone of the capillary output. The experimental data presented in the paper confirms such behavior of the x-ray radiation.
The combination of a table-top laser produced plasma X-ray source and spherically bent crystals for the soft X-ray region is used in traditional X-ray microscopy schemes. The X-ray source is well localized both spatially (approximately 20 micrometer) and temporally (1 ps - 10 ns, it depends on the used laser) and it is spectrally tunable in a relatively wide range (6 - 19 angstrom). High quality monochromatic ((delta) (lambda) /(lambda) approximately 10-5 - 10-3) images with high spatial resolution (up to approximately 4 micrometer) and in a large field of view (few mm) are presented. For many applications, these low-cost compact systems can offer a simple alternative to the larger installations which are usually used. It was demonstrated that the spherically bent crystals can be efficiently used in a wide ((Theta) equals 40 - 90 degrees) range of reflection angles, thus allowing wide wavelength selection. A very efficient concentration of monochromatic X-Ray radiation into different spot shapes (line, circle spot, etc) is demonstrated.
Propagation of the x-rays generated by a small incoherent source through the capillary, is studied using the Fresnel- Kirchhoff diffraction theory. The influence of the diffraction on the propagation is demonstrated. The diffraction is manifested by the appearance of the diffraction fringes in both the guide channel and the far- field zone of the capillary output. The experimental data which confirms such a behavior of the x-rays is also presented. The result give a confirmation for the interference effects recently observed in capillary optics.
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