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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]

High intensity laser-plasma interaction has attracted considerable interest for a number of years. The laser-plasma interaction is accompanied by generation of various charged particle beams, such as high-energy proton and ions with high charge to mass ratio (Q/M; same as multi-charged ions). Results of simultaneous novel measurements of electron-induced photonuclear neutrons (photoneutron), which are a diagnostic of the laser-plasma interaction, are proposed to use for optimization of the laser-plasma ion generation. The proposed method is demonstrated by the laser irradiation with the intensity of 1 x 1021 W/cm² on the metal foil target. The photoneutrons are measured by using NE213 liquid scintillation detectors. Heavy-ion signal is registered with the CR-39 track detector simultaneously. The measured signals of the electron-induced photoneutrons are well reproduced by using the Particle and Heavy Ion Transport code System. The results obtained provide useful approach for analyzing the various laser based ion beams. [ABSTRACT FROM AUTHOR]

We present the results of experiments on the generation of both high and low frequency electromagnetic radiation from the nonlinear interaction of intense laser beams with underdense plasmas. High frequency radiation is generated as a result of the reflection of a near-infrared laser beam by breaking plasma waves. In the proof-of-principle experiment, a 2 TW, 76 fs Ti:sapphire laser pulse was focused to generate wake waves, and a ~0.1 TW laser pulse was focused to collide with the electron density modulations. Frequencies of the reflected light were 56–110 times higher than that of the initial laser. The estimated number of photons per solid angle was 3×107 photons/sr. Low frequency radiation is emitted by the plasma as well. We found that the polarization of the radiation was similar to that of the driver laser. These properties are in accordance with the generation mechanism by relativistic solitons. [ABSTRACT FROM AUTHOR]

The possibility of phase-contrast imaging of nanostructures has been analyzed with the use of a femtosecond-laser plasma as a spatially coherent soft x-ray source and a LiF crystal as an x-ray detector having both the submicron spatial resolution in a wide field of view and a high contrast. It is demonstrated that the spatial coherence length of radiation in the wavelength range 1–13 nm at a distance of 30 cm from the femtosecond-laser plasma source is ≃1.5 μm. The achieved spatial coherence of the source is sufficient to obtain high-quality phase-contrast x-ray images of foils with various chemical compositions and a thickness of ≃100 nm. [ABSTRACT FROM AUTHOR]

As femtosecond laser pulses increase in intensity and decrease in duration, interaction between the focused laser radiation and a substance is followed by a sharp increase in the intensity of fast-electron, ion, and electromagnetic noise generation. In turn, the noise signals of X-ray detectors grow in amplitude and the signal-to-noise ratio in recording X-ray spectra of multiply charged ions approaches unity. A significant excess of the noise level over the useful signal is observed in plasmas generated by laser pulses with a power density of ≥1017 W/cm2. The most powerful effect of the above factors is exerted on X-ray spectra recorded by such electromagnetic equipment as CCD-based detectors, photoelectron amplifiers, etc. A new “mean-median” algorithm is described, with which it is possible to considerably increase the signal-to-noise ratio of CCD detectors used to measure X-ray spectra of femtosecond laser-produced plasma. [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]

The interaction of femtosecond laser pulses with SiO2 aerogel targets has been analyzed by x-ray spectroscopic methods. The use of an aerogel target with transparent grains makes it possible to considerably reduce the requirements on laser-pulse contrasts for which heating occurs without the formation of a preplasma. A nanoplasma with a density sevenfold higher than the solid-state density has been detected. © 2004 MAIK “Nauka/Interperiodica”. [ABSTRACT FROM AUTHOR]

It was established experimentally that the number and energy of fast ions in laser plasma increased with increasing angle of focusing laser radiation onto a flat target. Numerical calculations showed that the increase in angle of focusing brought the mean angle of incidence of laser radiation closer to the optimal angle corresponding to the maximal efficiency of the resonance absorption mechanism and, as a result, increased the fraction of absorbed laser energy in the energy of fast electrons and increased the number of fast electrons. In turn, the increase in the energy and number of fast electrons resulted in an increase in the number of fast electrons involved in the formation of a self-consistent electric field at the target edge and led to the growth of the field strength, which, eventually, was the reason for the increase in the number and energy of fast ions. © 2001 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

A portable (200x100x100 mm[sup 3]), high-luminosity, spherically bent crystal spectrometer was designed for measuring in a wide spectral range of 1.2-19.6 Å very low emissivity x-ray spectra of different clusters heated by 35 fs laser radiation. This spectrometer is associated with a custom design x-ray charge coupled device that features a large sensitive area (24.6x24.6 mm[sup 2]) and a small pixel size (24x24 μm[sup 2]). This apparatus provides simultaneous high spectral (λ/δλ∼1000-5000) and spatial (40-80 μm) resolution. A large (30x10 mm[sup 2]) open aperture mica crystal with R=100 mm is used as the dispersive and focusing element. The large tuneability of the spectrometer makes it possible to record high-resolution spectra of H-like ions of oxygen (CO[sub 2] clusters) in a spectral range of 15-17 Å, Ne-like like ions of Kr in a spectral range of 5-5.7 Å, and He-like spectra of Ar in a spectral range of 3.0-3.4 and 3.7-4.4 Å without any adjustment of the spectrometer setup. Thanks to the high luminosity (high collection efficiency) of the spectrometer, high quality spectra were obtained using only 15 mJ 2000 laser shots. © 2001 American Institute of Physics. [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]

Two-beam interferometric encoding of periodic lines of permanent color centers in LiF has been obtained by use of an intense and high spatially coherent soft x-ray laser beam. A spatial resolution of the lines less than 1 μm is demonstrated. We have used the 46.9 nm laser pulses (0.3 mJ, 1.7 ns at 0.2 Hz) produced in compact capillary discharges. Due to the low penetration depth of their radiation, their high brightness and spatial coherence, soft x-ray lasers can represent a powerful tool to encode integrated optical devices having low dimensionality and high spatial resolution inside optically transparent dielectrics, in extremely short exposure times. [ABSTRACT FROM AUTHOR]

The size of CO2 clusters, produced in a supersonic expansion of a mixed-gas of CO2/He or CO2/H2 through a three-staged conical nozzle designed based on the Boldarev's model, has been evaluated by measuring the angular distribution of light scattered from the clusters. The data are analyzed utilizing the Mie scattering theory, and the sizes of CO2 clusters are estimated as 0.22 μm and 0.25 μm for the cases of CO2/He and CO2/H2 gas mixtures, respectively. The results confirm that the Boldarev's model is reliable enough for the production of micron-sized clusters. [ABSTRACT FROM AUTHOR]