1,506 research outputs found
All-solid-state VUV frequency comb at 160 nm using high-harmonic generation in nonlinear femtosecond enhancement cavity
© 2019 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.We realized a solid-state-based vacuum ultraviolet frequency comb by harmonics
generation in an external enhancement cavity. Optical conversions were so far reported by
only using gaseous media. We present a theory that allows the most suited solid generation
medium to be selected for specific target harmonics by adapting the materialâs bandgap. We
experimentally use a thin AlN film grown on a sapphire substrate to realize a compact
frequency comb high-harmonic source in the Deep Ultraviolet (DUV)/Vacuum
Ultraviolet/Deep Ultraviolet (VUV) spectral range. By extending our earlier VUV source
[Opt. Express 26, 21900 (2018)] with the enhancement cavity, a sub-Watt level Ti:sapphire
femtosecond frequency comb is enhanced to 24 W stored average power, its 3rd, 5th, and 7th
harmonics are generated, and the targeted 5th harmonicâs power at 160 nm increased by two
orders of magnitude. The emerging nonlinear effects in the solid medium, together with
suitable intra-cavity dispersion management, support optimal enhancement and stable
locking. To demonstrate the realized frequency combâs spectroscopic ability, we report on the
beat measurement between the 3rd harmonic beam and a 266 nm CW laser reaching about 1
MHz accuracy.Peer ReviewedPostprint (published version
Light bending by nonlinear electrodynamics under strong electric and magnetic field
We calculate the bending angles of light under the strong electric and
magnetic fields by a charged black hole and a magnetized neutron star according
to the nonlinear electrodynamics of Euler-Heisenberg interaction. The bending
angle of light by the electric field of charged black hole is computed from
geometric optics and a general formula is derived for light bending valid for
any orientation of the magnetic dipole. The astronomical significance of the
light bending by magnetic field of a neutron star is discussed.Comment: drastically revised with conclusion change, reference added, version
to appear in JCA
High Energy Gamma Ray Production from Proton Induced Reactions on D, C, Zn, Pb at Incident Energies of 104, 145, and 195 MeV
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
Ferromagnetism in Oriented Graphite Samples
We have studied the magnetization of various, well characterized samples of
highly oriented pyrolitic graphite (HOPG), Kish graphite and natural graphite
to investigate the recently reported ferromagnetic-like signal and its possible
relation to ferromagnetic impurities. The magnetization results obtained for
HOPG samples for applied fields parallel to the graphene layers - to minimize
the diamagnetic background - show no correlation with the magnetic impurity
concentration. Our overall results suggest an intrinsic origin for the
ferromagnetism found in graphite. We discuss possible origins of the
ferromagnetic signal.Comment: 11 figure
Situationally edited empathy: an effect of socio-economic structure on individual choice
Criminological theory still operates with deficient models of the offender as agent, and of social influences on the agentâs decision-making process. This paper takes one âemotionâ, empathy, which is theoretically of considerable importance in influencing the choices made by agents; particularly those involving criminal or otherwise harmful action. Using a framework not of rational action, but of ârationalised actionâ, the paper considers some of the effects on individual psychology of social, economic, political and cultural structure. It is suggested that the climate-setting effects of these structures promote normative definitions of social situations which allow unempathic, harmful action to be rationalised through the situational editing of empathy. The âcrime is normalâ argument can therefore be extended to include the recognition that the uncompassionate state of mind of the criminal actor is a reflection of the self-interested values which govern non-criminal action in wider society
Interpreting Quantum Particles as Conceptual Entities
We elaborate an interpretation of quantum physics founded on the hypothesis
that quantum particles are conceptual entities playing the role of
communication vehicles between material entities composed of ordinary matter
which function as memory structures for these quantum particles. We show in
which way this new interpretation gives rise to a natural explanation for the
quantum effects of interference and entanglement by analyzing how interference
and entanglement emerge for the case of human concepts. We put forward a scheme
to derive a metric based on similarity as a predecessor for the structure of
'space, time, momentum, energy' and 'quantum particles interacting with
ordinary matter' underlying standard quantum physics, within the new
interpretation, and making use of aspects of traditional quantum axiomatics.
More specifically, we analyze how the effect of non-locality arises as a
consequence of the confrontation of such an emerging metric type of structure
and the remaining presence of the basic conceptual structure on the fundamental
level, with the potential of being revealed in specific situations.Comment: 19 pages, 1 figur
Star and Planet Formation with ALMA: an Overview
Submillimeter observations with ALMA will be the essential next step in our
understanding of how stars and planets form. Key projects range from detailed
imaging of the collapse of pre-stellar cores and measuring the accretion rate
of matter onto deeply embedded protostars, to unravelling the chemistry and
dynamics of high-mass star-forming clusters and high-spatial resolution studies
of protoplanetary disks down to the 1 AU scale.Comment: Invited review, 8 pages, 5 figures; to appear in the proceedings of
"Science with ALMA: a New Era for Astrophysics". Astrophysics & Space
Science, in pres
Survey of nucleon electromagnetic form factors
A dressed-quark core contribution to nucleon electromagnetic form factors is
calculated. It is defined by the solution of a Poincare' covariant Faddeev
equation in which dressed-quarks provide the elementary degree of freedom and
correlations between them are expressed via diquarks. The nucleon-photon vertex
involves a single parameter; i.e., a diquark charge radius. It is argued to be
commensurate with the pion's charge radius. A comprehensive analysis and
explanation of the form factors is built upon this foundation. A particular
feature of the study is a separation of form factor contributions into those
from different diagram types and correlation sectors, and subsequently a
flavour separation for each of these. Amongst the extensive body of results
that one could highlight are: r_1^{n,u}>r_1^{n,d}, owing to the presence of
axial-vector quark-quark correlations; and for both the neutron and proton the
ratio of Sachs electric and magnetic form factors possesses a zero.Comment: 43 pages, 17 figures, 12 tables, 5 appendice
Frame Theory for Signal Processing in Psychoacoustics
This review chapter aims to strengthen the link between frame theory and
signal processing tasks in psychoacoustics. On the one side, the basic concepts
of frame theory are presented and some proofs are provided to explain those
concepts in some detail. The goal is to reveal to hearing scientists how this
mathematical theory could be relevant for their research. In particular, we
focus on frame theory in a filter bank approach, which is probably the most
relevant view-point for audio signal processing. On the other side, basic
psychoacoustic concepts are presented to stimulate mathematicians to apply
their knowledge in this field
- âŠ