28 research outputs found
Energy dispersive x-ray spectroscopy for nanostructured thin film density evaluation
In this paper, we report on two fast and non-destructive methods for nanostructured film density evaluation based on a combination of energy dispersive x-ray spectroscopy for areal density measurement and scanning electron microscopy (SEM) for thickness evaluation. These techniques have been applied to films with density ranging from the density of a solid down to a few mg cm(-3), with different compositions and morphologies. The high resolution of an electron microprobe has been exploited to characterize non-uniform films both at the macroscopic scale and at the microscopic scale
Electron Acceleration by Relativistic Surface Plasmons in Laser-Grating Interaction
The generation of energetic electron bunches by the interaction of a short, ultraintense (I>1019 W/cm2) laser pulse with "grating" targets has been investigated in a regime of ultrahigh pulse-to-prepulse contrast (1012). For incidence angles close to the resonant condition for surface plasmon excitation, a strong electron emission was observed within a narrow cone along the target surface, with energy spectra peaking at 5-8 MeV and total charge of ∼100 pC. Both the energy and the number of emitted electrons were strongly enhanced with respect to simple flat targets. The experimental data are closely reproduced by three-dimensional particle-in-cell simulations, which provide evidence for the generation of relativistic surface plasmons and for their role in driving the acceleration process. Besides the possible applications of the scheme as a compact, ultrashort source of MeV electrons, these results are a step forward in the development of high-field plasmonics
Observation of ultrafast solid-density plasma dynamics using femtosecond X-ray pulses from a free-electron laser
The complex physics of the interaction between short pulse high intensity
lasers and solids is so far hardly accessible by experiments. As a result of
missing experimental capabilities to probe the complex electron dynamics and
competing instabilities, this impedes the development of compact laser-based
next generation secondary radiation sources, e.g. for tumor therapy
[Bulanov2002,ledingham2007], laboratory-astrophysics
[Remington1999,Bulanov2015], and fusion [Tabak2014]. At present, the
fundamental plasma dynamics that occur at the nanometer and femtosecond scales
during the laser-solid interaction can only be elucidated by simulations. Here
we show experimentally that small angle X-ray scattering of femtosecond X-ray
free-electron laser pulses facilitates new capabilities for direct in-situ
characterization of intense short-pulse laser plasma interaction at solid
density that allows simultaneous nanometer spatial and femtosecond temporal
resolution, directly verifying numerical simulations of the electron density
dynamics during the short pulse high intensity laser irradiation of a solid
density target. For laser-driven grating targets, we measure the solid density
plasma expansion and observe the generation of a transient grating structure in
front of the pre-inscribed grating, due to plasma expansion, which is an
hitherto unknown effect. We expect that our results will pave the way for novel
time-resolved studies, guiding the development of future laser-driven particle
and photon sources from solid targets
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Observation of Ultrafast Solid-Density Plasma Dynamics Using Femtosecond X-Ray Pulses from a Free-Electron Laser
The complex physics of the interaction between short-pulse ultrahigh-intensity lasers and solids is so far difficult to access experimentally, and the development of compact laser-based next-generation secondary radiation sources, e.g., for tumor therapy, laboratory astrophysics, and fusion, is hindered by the lack of diagnostic capabilities to probe the complex electron dynamics and competing instabilities. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that small-angle x-ray scattering of femtosecond x-ray free-electron laser pulses facilitates new capabilities for direct in situ characterization of intense short-pulse laser-plasma interactions at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short-pulse high-intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the preinscribed grating, due to plasma expansion. The density maxima are interleaved, forming a double frequency grating in x-ray free-electron laser projection for a short time, which is a hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets
Visualizing Ultrafast Kinetic Instabilities in Laser-Driven Solids using X-ray Scattering
Ultra-intense lasers that ionize and accelerate electrons in solids to near
the speed of light can lead to kinetic instabilities that alter the laser
absorption and subsequent electron transport, isochoric heating, and ion
acceleration. These instabilities can be difficult to characterize, but a novel
approach using X-ray scattering at keV energies allows for their visualization
with femtosecond temporal resolution on the few nanometer mesoscale. Our
experiments on laser-driven flat silicon membranes show the development of
structure with a dominant scale of ~60\unit{nm} in the plane of the laser
axis and laser polarization, and ~95\unit{nm} in the vertical direction with
a growth rate faster than . Combining the XFEL experiments
with simulations provides a complete picture of the structural evolution of
ultra-fast laser-induced instability development, indicating the excitation of
surface plasmons and the growth of a new type of filamentation instability.
These findings provide new insight into the ultra-fast instability processes in
solids under extreme conditions at the nanometer level with important
implications for inertial confinement fusion and laboratory astrophysics
Laser produced electromagnetic pulses : Generation, detection and mitigation
This paper provides an up-to-date review of the problems related to the generation, detection and mitigation of strong electromagnetic pulses created in the interaction of high-power, high-energy laser pulses with different types of solid targets. It includes new experimental data obtained independently at several international laboratories. The mechanisms of electromagnetic field generation are analyzed and considered as a function of the intensity and the spectral range of emissions they produce. The major emphasis is put on the gHz frequency domain, which is the most damaging for electronics and may have important applications. The physics of electromagnetic emissions in other spectral domains, in particular THz and MHz, is also discussed. The theoretical models and numerical simulations are compared with the results of experimental measurements, with special attention to the methodology of measurements and complementary diagnostics. Understanding the underlying physical processes is the basis for developing techniques to mitigate the electromagnetic threat and to harness electromagnetic emissions, which may have promising applications
Psychophysical and Electrophysiological Testing in Ocular Hypertension
Purpose. The purpose of this study was to compare psychophysical and electrophysiological testings in early optic nerve dysfunction in a group of clinically asymptomatic subjects with suspect ocular hypertension (OHT). Methods. Forty eyes of 40 patients with suspect OHT and asymmetrical horizontal cup/disc ratio (0.2/0.4), 22 eyes of 22 patients with open-angle glaucoma (OAG), and 40 eyes of 40 healthy controls were evaluated by using frequency-doubling technology perimetry (FDT), contrast sensitivity (CS), pattern electroretinography (PERG), and pattern visual-evoked potentials (VEP). The VEP were elicited by checkerboard stimuli with large (VEP 120), medium (VEP 45), and small (VEP 15) checks; then the values of the amplitude (A) and latency (L) of P100 peaks were studied. Receiver operator characteristic (ROC) curves were calculated to determine the sensitivity, specificity, and optimal cutoff points of abnormal values. A logistic regression analysis was performed to determine which tests were providing the most useful information. In addition, Kruskal-Wallis test was performed to test the differences between the control group and the OHT group. Results. VEP P100 peak latency (VEP L15 and VEP L45) and amplitude (VEP A120), PERG N95 peak amplitude, CS at medium spatial frequencies (CS 4SF), and FDT pattern standard deviation (PSD) yielded the greatest sensitivity (85.0 to 60.0%) and specificity (80.0 to 60.0%) ratio, displaying the largest ROC curve areas; whereas PERG N95 peak latency ROC curve had the smallest areas. Kruskal-Wallis test showed that most diagnostic tests were able to differentiate the OHT group from the control group. Stepwise logistic regression analysis identified VEP L15 (p < 0.001), CS 4SF (p = 0.023), FDT PSD (p = 0.032), and VEP A120 (p = 0.072) as tests that could be useful to distinguish controls from OHT. Conclusions. Our data confirm that psychophysical and electrophysiological tests are useful for early detection of patients at risk of developing OAG. (Optom Vis Sci 2011;88:E928-E939
Apoptosis Pathways Triggered by a Potent Antiproliferative Hybrid Chalcone on Human Melanoma Cells
TheWorld Health Organization reported that approximately 324,000 new cases of melanoma
skin cancer were diagnosed worldwide in 2020. The incidence of melanoma has been increasing over
the past decades. Targeting apoptotic pathways is a potential therapeutic strategy in the transition to
preclinical models and clinical trials. Some naturally occurring products and synthetic derivatives
are apoptosis inducers and may represent a realistic option in the fight against the disease. Thus,
chalcones have received considerable attention due to their potential cytotoxicity against cancer
cells. We have previously reported a chalcone containing an indole and a pyridine heterocyclic
rings and an -bromoacryloylamido radical which displays potent antiproliferative activity against
several tumor cell lines. In this study, we report that this chalcone is a potent apoptotic inducer
for human melanoma cell lines SK-MEL-1 and MEL-HO. Cell death was associated with mitochondrial
cytochrome c release and poly(ADP-ribose) polymerase cleavage and was prevented by a
non-specific caspase inhibitor. Using SK-MEL-1 as a model, we found that the mechanism of cell
death involves (i) the generation of reactive oxygen species, (ii) activation of the extrinsic and intrinsic
apoptotic and mitogen-activated protein kinase pathways, (iii) upregulation of TRAIL, DR4 and DR5,
(iv) downregulation of p21Cip1/WAF1 and, inhibition of the NF-B pathway