1,721,111 research outputs found
Schwinger Pair Production and Vacuum Birefringence around Highly Magnetized Neutron Stars
No full textAbstract: Highly magnetized neutron stars have magnetic fields of order of the critical field and can lead to measurable QED effects. We consider the Goldreich–Julian pulsar model with supercritical magnetic fields, induced subcritical electric fields, and a period of milliseconds. We then study the strong field physics, such as Schwinger pair production and the vacuum birefringence including the wrench effect, whose X-ray polarimetry will be observed in future space missions. © Pleiades Publishing, Ltd. 2023. ISSN 1063-7729, Astronomy Reports, 2023, Vol. 67, Suppl. 2, pp. S122–S128. Pleiades Publishing, Ltd., 2023.11Nsciescopu
Vacuum Birefringence in a Supercritical Magnetic Field and a Subcritical Electric Field
No full textRecent ultra-intense lasers of subcritical fields and proposed observations
of the x-rays polarization from highly magnetized neutron stars of
supercritical fields have attracted attention to vacuum birefringence, a unique
feature of nonlinear electrodynamics. We propose a formulation of vacuum
birefringence that incorporates the effects of the weaker electric field added
to the extremely strong magnetic field. To do so, we first derive a closed
analytical expression for the one-loop effective Lagrangian for the combined
magnetic and electric fields by using an explicit formula of the one-loop
effective Lagrangian for an arbitrarily strong magnetic field. We then employ
the expression to derive the polarization and magnetization of the vacuum, from
which the permittivity and permeability for weak probe fields are obtained.
Finally, we find the refractive indices and the associated polarization vectors
for the case of parallel magnetic and electric fields. The proposed formulation
predicts that an electric field along the magnetic field reduces the
birefringence and rotates the polarization vectors. Such effects should be
taken into account for accurate polarimetry of the x-rays from magnetized
neutron stars, which will prove the fundamental aspect of the strong field
quantum electrodynamics (QED) and explore the extreme fields of astrophysical
bodies
Generation of quasi-monoenergetic protons from a double-species target driven by the radiation pressure of an ultraintense laser pulse
No full textIn laser-driven proton acceleration, generation of quasi-monoenergetic proton beams has been considered a crucial feature of the radiation pressure acceleration (RPA) scheme, but the required difficult physical conditions have hampered its experimental realization. As a method to generate quasi-monoenergetic protons under experimentally viable conditions, we investigated using double-species targets of controlled composition ratio in order to make protons bunched in the phase space in the RPA scheme. From a modified optimum condition and three-dimensional particle-in-cell simulations, we showed by varying the ion composition ratio of proton and carbon that quasi-monoenergetic protons could be generated from ultrathin plane targets irradiated with a circularly polarized Gaussian laser pulse. The proposed scheme should facilitate the experimental realization of ultrashort quasi-monoenergetic proton beams for unique applications in high field science. © 2016 AIP Publishing LLC1441sciescopu
Polarization of amplified spontaneous emission in a plasma active medium
Full text linkWe present polarization measurement of a Ni-like Ag x-ray laser working in the transient collisional excitation
scheme. A calibrated membrane multilayer beam splitter was used to determine the energies of two mutually
perpendicular polarization components (s and p components). As a result, we observed a high degree of
polarization that fluctuated from shot to shot. The dominant polarization component switched from s to p
when pumping was made stronger. The measurement results are discussed from the point of view of the general
polarization theory and supported by a numerical simulation based on Maxwell-Bloch equations. The physical
processes causing the dominance of one polarization component are discussed in terms of pumping strength.
These results should extend the wave physics perspective on the amplification process, transforming a weak
random noise into a strong coherent radiation.3311Nsciescopu
First-principles simulation of the optical response of bulk and thin-film α-quartz irradiated with an ultrashort intense laser pulse
Full text linkA computational method based on a first-principles multiscale simulation has been used for calculating
the optical response and the ablation threshold of an optical material irradiated with an ultrashort intense
laser pulse. The method employs Maxwell’s equations to describe laser pulse propagation and timedependent
density functional theory to describe the generation of conduction band electrons in an optical
medium. Optical properties, such as reflectance and absorption, were investigated for laser intensities in
the range 1010W/cm2 to 21015W/cm2 based on the theory of generation and spatial distribution of the
conduction band electrons. The method was applied to investigate the changes in the optical reflectance
of a-quartz bulk, half-wavelength thin-film, and quarter-wavelength thin-film and to estimate their
ablation thresholds. Despite the adiabatic local density approximation used in calculating the
exchange–correlation potential, the reflectance and the ablation threshold obtained from our method
agree well with the previous theoretical and experimental results. The method can be applied to estimate
the ablation thresholds for optical materials, in general. The ablation threshold data can be used to
design ultra-broadband high-damage-threshold coating structures.111111sciescopu
Carrier-envelope-phase-dependent above-threshold ionization of xenon observed with multi-cycle laser pulses
No full textCarrier-envelope-phase (CEP)-dependent modulation was
measured in above-threshold ionization of xenon driven with 30-fs laser
pulses. We showed the dependence from the asymmetry map obtained using
a velocity map imaging spectrometer, up to 17 eV in photoelectron energy.
The dependence appeared to be linear with a slope of one photon energy
increase per CEP change of 2p and did not rely on the sign or the amount of
laser chirp. Our results indicated the existence of the quantum interference
between different multiphoton ionization paths.
© 2014 Optical Society of America1331sciescopu
Low-divergence relativistic proton jet from a thin solid target driven by an ultra-intense circularly polarized Laguerre–Gaussian laser pulse
No full text© 2020 IOP Publishing Ltd.We propose a new ion acceleration scheme of irradiating a thin solid target with an ultraintense circularly polarized Laguerre-Gaussian (LG) laser pulse. Three-dimensional particle-in-cell simulations are performed to demonstrate that this scheme can generate a low-divergence high-density relativistic proton jet. By this scheme, the number of protons emitted with a small angle (<1°) from the laser axis can be more than tens of times as high as that of the protons accelerated by a circularly polarized Gaussian pulse. The inward ponderomotive force of the LG pulse drives such a proton beam along the laser axis11Nsciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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