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  • 1
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    The scaling of electron and positron generation in intense laser-solid interactionsa) (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-05-28
    Description: This paper presents experimental scalings of the electrons and positrons produced by intense laser-target interactions at relativistic laser intensities (10 18 –10 20 W cm −2 ). The data were acquired from three short-pulse laser facilities with laser energies ranging from 80 to 1500 J. We found a non-linear (≈E L 2 ) scaling of positron yield [Chen et al ., Phys. Rev. Lett. 114 , 215001 (2015)] and a linear scaling of electron yield with the laser energy. These scalings are explained by theoretical and numerical analyses. Positron acceleration by the target sheath field is confirmed by the positron energy spectrum, which has a pronounced peak at energies near the sheath potential, as determined by the observed maximum energies of accelerated protons. The parameters of laser-produced electron-positron jets are summarized together with the theoretical energy scaling. The measured energy-squared scaling of relativistic electron-positron jets indicates the possibility to create an astrophysically relevant experimental platform with such jets using multi-kilojoule high intensity lasers currently under construction.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
    Electronic Resource
    Electronic Resource
    Nuclear magnetic resonance of J-coupled quadrupolar nuclei: Use of the tensor operator product basis (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 2908-2916 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In nuclear magnetic resonance (NMR) of I=1/2 nuclei that are scalar coupled to quadrupolar spins, a tensor operator product (TOP) basis set provides a convenient description of the time evolution of the density operator. Expressions for the evolution of equivalent I=1/2 spins, coupled to an arbitrary spin S〉1/2, were obtained by explicit algebraic density operator calculations in Mathematica, and specific examples are given for S=1 and S=3/2. Tensor operators are described by the convenient quantum numbers rank and order and this imparts to the TOP basis features that enable an intuitive understanding of NMR behavior of these spin systems. It is shown that evolution as a result of J coupling alone changes the rank of tensors for the coupling partner, generating higher-rank tensors, which allow efficient excitation of S-spin multiple-quantum coherences. Theoretical predictions obtained using the TOP formalism were confirmed using multiple-quantum filtered heteronuclear spin-echo experiments and were further employed to demonstrate polarization transfer directly to multiple-quantum transitions using the insensitive nucleus enhancement by polarization transfer pulse sequence. This latter experiment is the basis of two-dimensional heteronuclear correlation experiments and direct generation of multiple-quantum S-spin coherences can therefore be exploited to yield greater spectral resolution in such experiments. Simulated spectra and experimental results are presented. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1377025
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  • 3
    Electronic Resource
    Electronic Resource
    Electron conduction in molecular wires. I. A scattering formalism (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6849-6855 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We extend a model originally intended for the description of the scanning tunneling microscope (STM) current in molecular imaging of one-dimensional systems, to encompass the more general process of electron transfer between two reservoirs of states. In the STM problem, the reservoirs are naturally associated with the metal density of states of the electrodes. In the molecular electron transfer problem, the identification of the reservoirs with the Franck–Condon weighted density of vibrational states allows a number of fruitful connections with the theory of nonadiabatic electron transfer (ET) in molecules to be established. In this article, we present an exact procedure, based on Löwdin's partitioning technique, to determine the Green's function and the T matrix, relevant to the transport process. We obtain compact expressions for the conductance and the density of states in the limit of small applied voltage and low temperature, and discuss the important case where the molecular wire is described by a tight-binding Hamiltonian. Finally, we discuss some physical implications of the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468314
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  • 4
    Electronic Resource
    Electronic Resource
    Electron conduction in molecular wires. II. Application to scanning tunneling microscopy (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6856-6864 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We use scattering methods to calculate the conductance of molecular wires. We show that three kinds of wire length dependences of the conductance arise: the decay can be exponential, polynomial, or very slow, depending on whether the reservoir Fermi level lies far from, in, or at the edge of the molecular energy band. We use the formalism to discuss simple models of tip-induced pressure and of imaging in scanning tunneling microscopy (STM), and point out a paradoxical situation in which the current can decrease with increased tip pressure. We also consider the connection of this formalism with the conventional theory of intramolecular, nonadiabatic electron transfer (ET).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468315
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular electronics: Disordered molecular wires (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 5172-5178 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results for the effect of diagonal disorder on the conductance of molecular wires, using a simple one-dimensional tight-binding picture. We show that diagonal disorder affects three aspects of the conductance: (i) It produces large conductance fluctuations from wire to wire. (ii) It reduces the conductance in situations where the transfer would be resonant, and enhances the conductance when transfer is nonresonant. (iii) It gives near-exponential conductance decays with wire length.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467373
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  • 6
    Electronic Resource
    Electronic Resource
    Current-voltage characteristics of molecular wires: Eigenvalue staircase, Coulomb blockade, and rectification (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 7296-7305 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the current vs voltage curves (I–V characteristics) of a mesoscopic device consisting of two electrodes and a molecular wire. The wire Hamiltonian includes both electronic tunneling and Coulomb repulsion within a Hubbard model that is treated at the Hartree–Fock level. The inclusion of electron repulsion is an extension of our previous work that only considered the case of noninteracting electrons. We have found several important features in the calculated characteristics of the wire. These include (1) a staircaselike structure that strongly resembles that associated with Coulomb blockade in heterostructures and quantum dots, but that in the case of the wire is associated with the discrete nature of the molecular resonances; (2) regions of negative differential resistance associated with increased localization of the molecular resonances. Our theoretical model includes a consistent treatment of the conduction in the linear and nonlinear regimes which remains valid even when the device is operated close to resonance. These results can be particularly relevant for a comparison with recent experiments on molecular wires. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471396
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  • 7
    Electronic Resource
    Electronic Resource
    Method of reducing temperature gradients in contained gas flows and its application to the control of sample temperatures in a gas flow at 300 °C (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1952-1954 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple method of reducing temperature gradients in contained gas flows is described. The method is used to reduce the temperature gradient within a contained gas flow at 300 °C by a factor of about 100 and applied to the control of the temperature of a sample in the cavity of an EPR spectrometer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139498
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  • 8
    Electronic Resource
    Electronic Resource
    Constant-volume valve suitable for use in gas thermometry (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1294-1295 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An improved design for a simple constant-volume valve is described. Experience with the valve over several years of use confirms that it is suitable for use in gas thermometry or similar applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1137996
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  • 9
    Electronic Resource
    Electronic Resource
    Measurement of thermal diffusivity of thin films and foils using a laser scanning microscope (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 176-181 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel method for measuring the thermal diffusivity of free-standing foils and thin films is described and has been used to measure the thermal diffusivity of gold and amorphous silicon foils. The method involves scanning the surface of the film using a sinusoidally modulated, finely focused laser beam and monitoring the thermovoltage developed at a fixed point on its surface. A thermal wave spreads out from the point where the laser spot irradiates the foil which depends only on the thermal properties of the film material and the modulation frequency. Measuring the phase of the thermovoltage, which in turn is generated due to the thermal wave, the thermal diffusivity of the films was determined. The experiments were performed in vacuum so that convective heat losses could be neglected. The thermal diffusivity of 100-nm-thick gold foils was found to be 1.17×10−4 m2/s and that of 200-nm-thick amorphous silicon foils was determined to be 0.062×10−4 m2/s. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145255
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  • 10
    Electronic Resource
    Electronic Resource
    Coaxial ion beam/infrared laser beam spectrometer for investigating infrared spectra of doubly positively charged molecules (molecular dications) (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 241-254 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have constructed an apparatus for studying the infrared spectra of molecules with a doubly positive charge (molecular dications). The spectroscopic transitions were recorded indirectly by means of observing a change in the fragmentation rate of the molecular dication when a transition was in resonance. The design and performance of the spectrometer are described, with particular emphasis on the sensitivity achieved for detecting infrared spectra and Zeeman split infrared spectra. The operation and calibration of the spectrometer are discussed and sample results for DCl2+ are presented. It is shown that we achieve the maximum possible signal/noise ratio that could be achieved in this type of experiment. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1428638
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