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  • 1
    Electronic Resource
    Electronic Resource
    Dynamic nuclear magnetic resonance frequency shifts for spin 1/2 nuclei coupled to efficiently relaxed spin(approximately-greater-than)1/2 nuclei (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5181-5189 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently, it has been demonstrated that outside of the extreme narrowing regime, interference (cross-correlation) of dipole–dipole and quadrupole interactions can result in visually dramatic second order nuclear magnetic resonance (NMR) frequency shifts for spin one-half nuclei which are scalar coupled to spin-one nuclei. In the work presented here, the consequences of this dynamic frequency shift are examined in greater detail. Previous work has also shown that interferences between quadrupole and anisotropic chemical shieldings can provide significant differential line broadening across the spin one-half multiplet. These complementary calculations are extended to embody the general two spin system, I=1/2, S(approximately-greater-than)1/2, in the high field limit where extreme narrowing does not obtain. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469243
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  • 2
    Electronic Resource
    Electronic Resource
    Evidence for a nuclear hexadecapole interaction in the hyperfine spectrum of LiI (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2431-2436 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The molecular beam electric resonance technique has been used to examine the hyperfine spectrum of 7LiI to determine the nuclear hexadecapole interaction of the iodine nucleus. The nuclear magnetic octupole interaction was also considered but found to be marginally significant. A total of 172 transitions in vibrational states 0-3 and rotational states 1-6 have been included in a fit to determine the iodine nuclear quadrupole, spin-rotation, and hexadecapole interactions, the lithium quadrupole and spin-rotation interactions, and the tensor and scalar parts of the spin-spin interaction. Vibration and rotation dependencies of these constants have been determined. The results include: eHh=−0.0151(30), eQIqI=−194351.212(17)−8279.521(46)(v+1/2)+100.616(34)(v+1/2)2−0.3949(73)(v+1/2)3−6.41977(50)J(J+1)+0.10593(33)(v+1/2)J(J+1),eQLiqLi=172.613(52)−3.26(14)(v+1/2)+0.00145(87)J(J+1),cI=6.80260(32)+0.00303(49)(v+1/2)−0.000118(13)J(J+1), cLi=0.75872(72)−0.0088(11)(v+1/2), c3=0.62834(68)−0.0050(11)(v+1/2), c4=0.06223(36)+0.00041(26)(v+1/2), and eΩIωI′=0.000112(73), all in kHz with one standard deviation uncertainties for the last 2 digits in ( ). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477972
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  • 3
    Electronic Resource
    Electronic Resource
    Supernova hydrodynamics experiments on the Nova laser : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1994-2003 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In studying complex astrophysical phenomena such as supernovae, one does not have the luxury of setting up clean, well-controlled experiments in the universe to test the physics of current models and theories. Consequently, creating a surrogate environment to serve as an experimental astrophysics testbed would be highly beneficial. The existence of highly sophisticated, modern research lasers, developed largely as a result of the world-wide effort in inertial confinement fusion, opens a new potential for creating just such an experimental testbed utilizing well-controlled, well-diagnosed laser-produced plasmas. Two areas of physics critical to an understanding of supernovae are discussed that are amenable to supporting research on large lasers: (1) compressible nonlinear hydrodynamic mixing and (2) radiative shock hydrodynamics. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872341
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  • 4
    Electronic Resource
    Electronic Resource
    Tabletop x-ray lasersf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1744-1752 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Details of schemes for two tabletop size x-ray lasers that require a high-intensity short-pulse driving laser are discussed. The first is based on rapid recombination following optical-field ionization. Analytical and numerical calculations of the output properties are presented. Propagation in the confocal geometry is discussed and a solution for x-ray lasing in Li-like N at 247 A(ring) is described. Since the calculated gain coefficient depends strongly on the electron temperature, the methods of calculating electron heating following field ionization are discussed. Recent experiments aimed at demonstrating lasing in H-like Li at 135 A(ring) are discussed along with modeling results. The second x-ray laser scheme is based on the population inversion obtained during inner-shell photoionization by hard x rays. This approach has significantly higher-energy requirements, but lasing occurs at very short wavelengths (λ≤15 A(ring)). Experiments that are possible with existing lasers are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870936
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  • 5
    Electronic Resource
    Electronic Resource
    Ionization-induced refraction in recombination x-ray lasers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 414-419 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ionization-induced refraction is examined in regimes relevant to recent and planned recombination x-ray lasing experiments [D. C. Eder et al., Phys. Plasmas 1, 1744 (1994)]. A model that self-consistently evolves the laser radiation as it ionizes a neutral gas is presented. The model allows for multiple ionization stages and for spatial variations in the neutral gas density appropriate for studying gas jets and laser evaporated gases. The length of highly stripped plasma is calculated in H-like Li and Li-like N systems, where the conditions are appropriate for recombination. It is found that for a given pump power there is always an optimal spot size and focal position with respect to the gas jet, which minimizes refraction and maximizes the length for which gain is possible. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871868
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  • 6
    Electronic Resource
    Electronic Resource
    The scaling of Ne-like x-ray laser schemes to short wavelength (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 666-670 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The driver and target parameters required to extend the successful results from an exploding foil Ne-like-Se soft x-ray laser at 206 A(ring) towards wavelengths of 40 A(ring) are investigated. The power requirements are found to scale as λ−4, which is quite costly. The principal constraint is the refraction of the x-ray laser beam in these high density, single pass, exploding foil targets. Correcting mirrors or nonrefracting target designs could reduce this costly scaling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866797
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  • 7
    Electronic Resource
    Electronic Resource
    Beam optics of exploding foil plasma x-ray lasers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 184-192 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In soft x-ray lasers, amplification is achieved as the x rays propagate down a long narrow plasma column. Refraction, due to electron density gradients, tends to direct the x-rays out of high density regions. This can have the undesirable effect of shortening the distance that the x ray stay within the plasma, thereby limiting the amount of amplification. The exploding foil design lessens refraction, but does not eliminate it. In this paper, a quantitative analysis of propagation and amplification in an exploding foil x-ray laser is presented. The density and gain profiles within the plasma are modeled in an approximate manner, which enables considerable analytic progress. It is found that refraction introduces a loss term to the laser amplification. The beam pattern from a parabolic gain profile laser has a dominant peak on the x-ray laser axis. The pattern from a quartic gain profile having a dip on-axis can produce a profile with off-axis peaks, in better agreement with recent experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866565
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  • 8
    Electronic Resource
    Electronic Resource
    Multidimensional similarity models for exploding foils (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3102-3108 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general derivation of the Gaussian, isothermal similarity equations for multidimensional hydrodynamic expansions is presented. Analytical solutions for the cases of constant heating and adiabatic flow for planar, cylindrical, and spherical expansions are given. An energy integral is derived for general multidimensional adiabatic flows. For two-dimensional adiabatic expansions, a second invariant of the motion is demonstrated. It is shown that this invariant gives the asymptotic shape of a Gaussian object in terms of its initial shape. A simple model for laser heating of an exploding foil is described and the asymptotic form of the corresponding solutions are given for two and three dimensions. The similarity solutions are compared with two-dimensional numerical hydrodynamic simulations for an example of an exploding foil, designed to produce a recombination x-ray laser.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866965
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  • 9
    Electronic Resource
    Electronic Resource
    Hydrodynamics of exploding foil x-ray lasers (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3813-3822 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An accurate simple model for the hydrodynamics of laser heated exploding foils is presented. Particular emphasis is given to applications in the design of soft x-ray lasers. The model predicts the conditions in the foil plasma (e.g., temperature, density, and scale length), given the experimental parameters (e.g., optical laser intensity, laser pulse duration, target thickness, and target composition). The simple model is based on an isothermal, homogeneous expansion similarity solution of the ideal hydrodynamic equations. Both analytical and numerical solutions of the similarity equations are studied. The numerical solutions agree closely with computational hydrodynamic simulations at times of interest—after the laser burns through the foil. Analytic solutions for constant intensity laser irradiation provide useful power-law scaling relations between the input laser and target parameters and the plasma variables. The simple model is a powerful design tool that reproduces the essential results of more expensive and time-consuming simulations over a large and important range of parameter space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865764
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  • 10
    Electronic Resource
    Electronic Resource
    Absence of Dicke narrowing in x-ray laser plasmas? (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 4495-4498 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Present x-ray laser plasmas are in the intermediate coupling regime (0.1〈Γ〈4, Γ≡Z2e2/kTa, with a the ion sphere radius), where the binary collision based arguments of low density plasma kinetic theory can be misleading. The difficulty of modeling the spectral output from neonlike lasers at wavelengths near 200 A(ring) has led to the suggestion, based on a low density, electron screened, plasma model, that collisional ("Dicke'') narrowing may be important. Molecular dynamics results, which include ion collisions and screening effects, are presented here. They indicate that the free-particle Doppler approximation is still quite accurate for λ∼200 A(ring) and Γ(approximately-less-than)1. Collisional narrowing will become important at somewhat stronger couplings (Γ∼5) and at this wavelength the diffusion approximation is reasonable for Γ(approximately-greater-than)10. Collisional narrowing is found to be small even for the higher density (Γ≈4) nickel-like lasers operating near 45 A(ring).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860565
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