Biomedical subjects

A Ya Faenov

Publications and source records attributed to A Ya Faenov.

8 recordsLinked to original sources

PubMed2006

Spectroscopic characterization of an ultrashort-pulse-laser-driven Ar cluster target incorporating both Boltzmann and particle-in-cell models.

A model that solves simultaneously both the electron and atomic kinetics was used to generate a synthetic He alpha and satellite x-ray spectra to characterize a high intensity ultrashort laser driven Ar cluster target experiment. In particular, level populations were obtained from a detailed collisional-radiative model where collisional rates were computed from a time varying electron distribution function obtained from the solution of the zero-dimensional Boltzmann equation. In addition, a particle-in-cell simulation was used to model the laser interaction with the cluster target and provided the initial electron energy distribution function (EEDF) for the Boltzmann solver. This study suggests that a high density average, high, of 3.2 x 10(20) cm(-3) was held by the system for a time, delta tau, of 5.7 ps, and during this time the plasma was in a highly nonequilibrium state in both the EEDF and the ion level populations.

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PubMed2006

X-ray spectroscopy of 1 cm plasma channels produced by self-guided pulse propagation in elongated cluster jets.

We diagnose the self-channeled propagation of intense femtosecond pulses over an extended distance in a N2O cluster gas target using high resolution kilovolt x-ray pinhole images of the channel and spatially resolved x-ray spectra. The x-ray images are consistent with femtosecond optical scattering, shadowgraphy, and interferometry images. We observe extended plasma channels (approximately 9 mm) limited either by the cluster jet length or by absorption, for injected laser intensities in the range of 10(16)-10(17) W/cm2. Spectral line shapes for the OVII 1s2-1s3p and OVIII 1s-2p transitions (at 1.8627 and 1.8969 nm, respectively) show significant broadening to the blue side and with truncated emission on the red side. We attribute this effect to Doppler blueshifted emission from fast ions from exploding clusters moving toward the spectrometer; redshifted emission from the opposite side of the cluster is absorbed.

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PubMed2005

Temperature determination using Kalpha spectra from M -shell Ti ions.

The compact multipulse terawatt (COMET) laser facility at LLNL was used to irradiate Al-coated 2-50 microm Ti foils with approximately 10(19) W cm(-2) , 500 fs, 3-6 J laser pulses. Laser-plasma interactions on the front side of the target generate hot electrons with sufficient energy to excite inner-shell electrons in Ti, creating Kalpha emission which has been measured using a focusing spectrometer with spatial resolution aimed at the back surface of the targets. The spatial extent of the emission varies with target thickness. The high spectral resolution (lambda/Deltalambda approximately equal to 3800) is sufficient to measure broadening of the Kalpha emission feature due to the emergence of blueshifted satellites from ionized Ti in a heated region of the target. A self-consistent-field model is used to spectroscopically diagnose thermal electron temperatures up to 40 eV in the strongly coupled Ti plasmas.

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PubMed2005

Measurement of 2l-nl' x-ray transitions from approximately 1 microm Kr clusters irradiated by high-intensity femtosecond laser pulses.

X-ray line emission from 2l-nl' transitions in Ne-like Kr and nearby ions has been observed from approximately 1 microm Kr clusters irradiated by fs-scale laser pulses at the JAERI facility in Kyoto, Japan. The incident laser intensity reached 10(19) W/cm2, with pulse energies from 50 to 300 mJ and pulse durations from 30 to 500 fs. The dependence of the x-ray spectral features and intensity on the incident laser intensity is rather weak, indicating that the 1-2 ps cluster lifetimes limit the number of ions beyond Ne-like Kr that can be produced by collisional ionization. Lines from F- to Al-like Kr emitted from the cluster plasmas have been identified using data from the relativistic multiconfiguration flexible atomic code. A collisional-radiative model based on these data has been constructed and used to determine that the cluster plasma has electron densities near 10(22) cm(-3), temperatures of a few hundred eV, and hot electron fractions of a few percent.

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PubMed2004

Analysis of high- n dielectronic Rydberg satellites in the spectra of Na -like Zn XX and Mg -like Zn XIX.

We have observed spectra from highly charged zinc ions in a variety of laser-produced plasmas. Spectral features that are Na - and Mg -like satellites to high- n Rydberg transitions in the Ne -like Zn XXI spectrum are analyzed and modeled. Identifications and analysis are made by comparison with highly accurate atomic structure calculations and steady state collisional-radiative models. Each observed Zn XX and Zn XIX feature comprises up to approximately 2 dozen individual transitions, these transitions are excited principally by dielectronic recombination through autoionizing levels in Na - and Mg -like Zn19+ and Zn18+. We find these satellites to be ubiquitous in laser-produced plasmas formed by lasers with pulse lengths that span four orders of magnitude, from 1 ps to approximately 10 ns. The diagnostic potential of these Rydberg satellite lines is demonstrated.

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PubMed2003

Influence of optical thickness and hot electrons on Rydberg spectra of Ne-like and F-like copper ions.

Spectra in the 7.10 to 8.60 A range from highly charged copper ions are observed from three different laser-produced plasmas (LPPs). The LPPs are formed by a 15-ns Nd:glass laser pulse (type I: E(pulse)=1-8 J, lambda=1.064 microm), a 1-ps Nd:glass laser pulse (type II: E(pulse)=1 J, lambda=1.055 microm), and a 60-fs Ti:sapphire laser pulse (type III: E(pulse)=800 mJ, lambda=790 nm). The spectra of high-n (n<or=14) transitions in highly charged copper ions, Cu19+ to Cu21+, are recorded with a high energy resolution (lambda/deltalambda=3000-8000) spectrometer using a spherically bent mica or quartz crystal. Collisional-radiative models are computed for the emission from each plasma. The sensitivity of the model spectra to opacity effects and to populations of superthermal electrons is studied. For the type I LPPs, opacity effects, treated with escape factors, are necessary to get the correct relative intensities of high-n (n=5, 6) Ne-like Cu19+ emission features. In the case of the type II LPPs, the contrast between the laser prepulse and the main pulse has been varied from low, I(main)/I(pp)=7 x 10(4), to high, I(main)/I(pp)=3.8 x 10(7). For plasmas from low contrast shots, we find good agreement between the observed spectra and optically thin simulations with bulk electron temperatures T(bulk)=0.4 keV and a small population of superthermal electrons (T(hot)=5.0 keV) that is f(hot)<or=10(-5) of the bulk electron population. For high-contrast type II LPPs, we find higher densities and a combination of f(hot) approximately 10(-5) and escape factors best describes the data. For the type III 60-fs LPPs, a population of superthermal electrons (T(hot) approximately 5 keV) that is approximately 5 x 10(-5) of the bulk electron population (T(bulk) approximately 0.2 keV) is required to reproduce the observed spectra. The effect of both escape factors and hot electrons in the CR models is to increase the ionization balance and dramatically increase the number of strong lines for each ion considered. We have studied both opacity effects and hot-electron influence on high-n transitions of highly charged Ne-, F-, and O-like ions.

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PubMed2002

Charge-exchange-induced two-electron satellite transitions from autoionizing levels in dense plasmas.

Order-of-magnitude anomalously high intensities for two-electron (dielectronic) satellite transitions, originating from the He-like 2s(2) 1S0 and Li-like 1s2s(2) (2)S(1/2) autoionizing states of silicon, have been observed in dense laser-produced plasmas at different laboratories. Spatially resolved, high-resolution spectra and plasma images show that these effects are correlated with an intense emission of the He-like 1s3p 1P-1s(2) 1S lines, as well as the K(alpha) lines. A time-dependent, collisional-radiative model, allowing for non-Maxwellian electron-energy distributions, has been developed for the determination of the relevant nonequilibrium level populations of the silicon ions, and a detailed analysis of the experimental data has been carried out. Taking into account electron density and temperature variations, plasma optical-depth effects, and hot-electron distributions, the spectral simulations are found to be not in agreement with the observations. We propose that highly stripped target ions (e.g., bare nuclei or H-like 1s ground-state ions) are transported into the dense, cold plasma (predominantly consisting of L- and M-shell ions) near the target surface and undergo single- and double-electron charge-transfer processes. The spectral simulations indicate that, in dense and optically thick plasmas, these charge-transfer processes may lead to an enhancement of the intensities of the two-electron transitions by up to a factor of 10 relative to those of the other emission lines, in agreement with the spectral observations.

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PubMed2002

Spatially resolved x-ray spectroscopy investigation of femtosecond laser irradiated Ar clusters.

High temperature plasmas have been created by irradiating Ar clusters with high intensity 60-fs laser pulses. Detailed spectroscopic analysis of spatially resolved, high resolution x-ray data near the He(alpha) line of Ar is consistent with a two-temperature collisional-radiative model incorporating the effects of highly energetic electrons. The results of the spectral analysis are compared with a theoretical hydrodynamic model of cluster production, as well as interferometric data. The plasma parameters are notably uniform over one Rayleigh length (600 microm).

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