675 research outputs found
Indirect monitoring shot-to-shot shock waves strength reproducibility during pump-probe experiments
No full textT. A. Pikuz, A. Ya. Faenov, N. Ozaki, N. J. Hartley, B. Albertazzi, T. Matsuoka, K. Takahashi, H. Habara, Y. Tange, S. Matsuyama, K. Yamauchi, R. Ochante, K. Sueda, O. Sakata, T. Sekine, T. Sato, Y. Umeda, Y. Inubushi, T. Yabuuchi, T. Togashi, T. Katayama, M. Yabashi, M. Harmand, G. Morard, M. Koenig, V. Zhakhovsky, N. Inogamov, A. S. Safronova, A. Stafford, I. Yu. Skobelev, S. A. Pikuz, T. Okuchi, Y. Seto, K. A. Tanaka, T. Ishikawa, and R. Kodama, "Indirect monitoring shot-to-shot shock waves strength reproducibility during pump–probe experiments", Journal of Applied Physics 120, 035901 (2016) https://doi.org/10.1063/1.4958796.We present an indirect method of estimating the strength of a shock wave, allowing on line monitoring of its reproducibility in each laser shot. This method is based on a shot-to-shot measurement of the X-ray emission from the ablated plasma by a high resolution, spatially resolved focusing spectrometer. An optical pump laser with energy of 1.0 J and pulse duration of ∼660 ps was used to irradiate solid targets or foils with various thicknesses containing Oxygen, Aluminum, Iron, and Tantalum. The high sensitivity and resolving power of the X-ray spectrometer allowed spectra to be obtained on each laser shot and to control fluctuations of the spectral intensity emitted by different plasmas with an accuracy of ∼2%, implying an accuracy in the derived electron plasma temperature of 5%-10% in pump-probe high energy density science experiments. At nano- and sub-nanosecond duration of laser pulse with relatively low laser intensities and ratio Z/A ∼ 0.5, the electron temperature follows Te ∼ Ilas2/3. Thus, measurements of the electron plasma temperature allow indirect estimation of the laser flux on the target and control its shot-to-shot fluctuation. Knowing the laser flux intensity and its fluctuation gives us the possibility of monitoring shot-to-shot reproducibility of shock wave strength generation with high accuracy
Photoluminescent radiation-induced color centers in lithium fluoride for detection of pulsed 10 keV XFEL beam
No full textImages of the Spring-8 Angstrom Compact free electron LAser (SACLA) 10 keV pulsed (10 fs) beam were recorded in a lithium fluoride (LiF) crystal by exploiting visible photoluminescence of radiation-induced color centers (CCs). Photoluminescent beam images stored in LiF, irradiated at several energies from 0.04 to 0.8 J, were acquired by a fluorescence optical microscope and processed with an algorithm developed in Matlab, allowing to reconstruct the transversal beam fluence distribution
Photoluminescence properties and characterization of LiF-based imaging detector irradiated by 10 keV XFEL beam
No full textWe present the study of optical and spectral properties of radiation-induced stable point defects, known as color centers (CCs), in lithium fluoride (LiF) for the detection of 10 keV XFEL beam at Spring-8 Angstrom Compact free electron LAser (SACLA) in Japan. A thick LiF crystal was irradiated in four spots with 10 keV XFEL beam (pulse duration = 10 fs) with different number of accumulated shots. After irradiation the colored-LiF spots were characterized with an optical microscope in fluorescence mode and their photoluminescence intensity and spectra were analyzed
Rising the signal-to-noise ratio in X-ray spectra of femtosecond laser-produced plasmas using the "mean-median" algorithm
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Extracting ion emission lines from femtosecond-laser plasma x-ray spectra heavily contamined by spikes
No full textA laser-produced plasma X-ray source for contact microscopy
No full textA promising field of application of the X-ray radiation generated by intense laser-matter interaction is the contact-microscopy of biological samples. In order to optimize the yield on the desired spectral window, it is fundamental to have an accurate characterization of this emitted radiation. To this purpose, an experimental campaign is underway with the three-nanosecond phosphate Nd:glass laser at the ABC laboratory in ENEA. The plasma was generated by irradiating solid targets with energy up to 30 J, and intensity on target up to 1014 Wcm−2. A transmission grating provided low-resolution spectra of a wide spectral range (2–50 Å). This covered also the so-called "water window" region, namely the spectral region between Oxygen and Carbon K-absorption edges (23 to 44 Å) where the absorption of carbon is ten times that of oxygen, and for this reason is of high interest for the contact-microscopy application. The X-ray yield in this spectral region was also monitored by a PIN diode filtered with 0.5 μm vanadium foil and coupled with a grazing-incidence copper mirror. A spherically-bent mica crystal was used to obtain high resolution spectra of the region going from 5.1 to 5.8 Å. This narrow spectral range was analyzed for determining the temperature of the produced plasma through the identification of different lines and of their intensity
Role of the wall ablation in the operation of a 46.9 nm Ar capillary discharge soft x-ray laser
No full textA capillary discharge pumped soft x-ray laser operating at 46.9 nm on the 3p-3s transition of the Ne-like Ar has been realized by pumping the active medium with a relatively slow current pulse (dI/dt ≈ 6-1011 A/s). In order to study the role of the ablation in the production of the laser effect, the intensity of the amplified 46.9 nm line has been investigated using the same pumping current pulses in the plastic (polyacetal) and ceramic (Al2O3). We showed that the ablation of the capillary walls is unfavorable both for the compression and stability of the plasma and consequently for the soft x-ray laser production. The amplification and lasing effects are observed only in the ceramic channel. The measurements of the line intensity at 46.9 nm showed the lasing with a gain-length product of ≈ 9, a laser pulse energy of ≈ 5 μJ, a pulse duration of 1.3 ns and a beam divergence of ≈ 3.5 mrad. In addition, effect of the scaling of the time of lasing with the initial plasma diameter was demonstrated experimentally and compared with a one-dimensional MHD model
Photoluminescent colour centres in lithium fluoride film imaging detectors for monochromatic hard X-rays
No full textPassive solid-state detectors based on the optical reading of the visible photoluminescence (PL) emitted by radiation-induced F2 and F+3 colour centres in lithium fluoride (LiF) have been successfully tested for X-ray imaging. They are characterized by high spatial resolution, wide dynamic range, large field of view, non-destructive readout capability, and simplicity of use. Optically-transparent polycrystalline LiF films of increasing thickness (0.5 and 1.1 μm) grown by thermal evaporation on glass and Si(100) substrates were irradiated with monochromatic 7 keV X-rays at several doses from 13 to 1.4 × 103 Gy at the SOLEIL synchrotron facility. For all the LiF films, the spectrally-integrated visible PL signal intensity was found to depend linearly on the irradiation dose, with films grown on Si(100) substrates exhibiting up to a 50% higher response compared to those grown on glass. The minimum dose of 13 Gy was detected, despite the low thickness of the irradiated films. A spatial resolution of (0.54 ± 0.02) μm was obtained in edge-enhancement imaging experiments conducted by placing an Au mesh in front of the LiF film detectors
Advanced spectroscopic investigation of colour centres in LiF crystals irradiated with monochromatic hard x-rays
No full textNominally-pure lithium fluoride (LiF) crystals were irradiated with monochromatic hard x-rays of energy 5, 7, 9 and 12 keV at the METROLOGIE beamline of the SOLEIL synchrotron facility, in order to understand the role of the selected x-ray energy on their visible photoluminescence (PL) response, which is used for high spatial resolution 2D x-ray imaging detectors characterized by a wide dynamic range. At the energies of 7 and 12 keV the irradiations were performed at five different doses corresponding to five uniformly irradiated areas, while at 5 and 9 keV only two irradiations at two different doses were carried out. The doses were planned in a range between 4 and 1.4 × 103 Gy (10.5 mJ cm−3 to 3.7 J cm−3), depending on the x-ray energy. After irradiation at the energies of 7 and 12 keV, the spectrally-integrated visible PL intensity of the F2 and F3+ colour centres (CCs) generated in the LiF crystals, carefully measured by fluorescence microscopy under blue excitation, exhibits a linear dependence on the irradiation dose in the investigated dose range. This linear behaviour was confirmed by the optical absorption spectra of the irradiated spots, which shows a similar linear behaviour for both the F2 and F3+ CCs, as derived from their overlapping absorption band at around 450 nm. At the highest x-ray energy, the average concentrations of the radiation-induced F, F2 and F3+ CCs were also estimated. The volume distributions of F2 defects in the crystals irradiated with 5 and 9 keV x-rays were reconstructed in 3D by measuring their PL signal using a confocal laser scanning microscope operating in fluorescence mode. On-going investigations are focusing on the results obtained through this z-scanning technique to explore the potential impact of absorption effects at the excitation laser wavelength
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