1,782 research outputs found
Q-switched laser damage of infrared nonlinear materials
Q-switched laser-damage thresholds have been determined for six materials (proustite – Ag3AsS3, pyrargyrite – Ag3SbS3, cinnabar – HgS, silver thiogallate – AgGaS2, tellurium – Te, and gallium arsenide – GaAs) of interest for nonlinear optics in the medium infrared. Four TEM00 mode lasers were employed with outputs at wavelengths of 694 nm, 1.06, 2.098, and 10.6 µm. Damage has been found to be confined to the surface of the crystals and occurs for radiation intensities between 3 and 75 MW/cm2. Particular care is needed in the cutting and polishing of tellurium crystals if a high-damage threshold is to be achieved
Singly-resonant proustite parametric oscillator tuned from 1.22µm to 8.5µm
A singly resonant parametric oscillator based on proustite has been operated for the first time. The device was pumped by a Q-switched neodymium (1.065µm) laser in a noncollinear phase-matching geometry. The output has been tuned over the wavelength range 1.22-8.5µm. The idler power was typically ~100W in a bandwidth of ~1/cm
Active Q-switch technique for producing high laser power in a single longitudinal mode
A Pockels-cell Q switch has been operated in a manner analogous to a saturable absorber, thus allowing the simple and reliable selection of a single longitudinal mode. A TEMoo mode Nd-CaWO4 laser has produced 400kW pulses in a single longitudinal mode with a shot-to-shot frequency stability of about 0.01 /cm
Advances in the proposed electromagnetic zero-point field theory of inertia
A NASA-funded research effort has been underway at the Lockheed Martin
Advanced Technology Center in Palo Alto and at California State University in
Long Beach to develop and test a recently published theory that Newton's
equation of motion can be derived from Maxwell's equations of electrodynamics
as applied to the zero-point field (ZPF) of the quantum vacuum. In this
ZPF-inertia theory, mass is postulated to be not an intrinsic property of
matter but rather a kind of electromagnetic drag force that proves to be
acceleration dependent by virtue of the spectral characteristics of the ZPF.
The theory proposes that interactions between the ZPF and matter take place at
the level of quarks and electrons, hence would account for the mass of a
composite neutral particle such as the neutron. An effort to generalize the
exploratory study of Haisch, Rueda and Puthoff (1994) into a proper
relativistic formulation has been successful. Moreover the principle of
equivalence implies that in this view gravitation would also be electromagnetic
in origin along the lines proposed by Sakharov (1968). With regard to exotic
propulsion we can definitively rule out one speculatively hypothesized
mechanism: matter possessing negative inertial mass, a concept originated by
Bondi (1957) is shown to be logically impossible. On the other hand, the linked
ZPF-inertia and ZPF-gravity concepts open the conceptual possibility of
manipulation of inertia and gravitation, since both are postulated to be
electromagnetic phenomena. It is hoped that this will someday translate into
actual technological potential. A key question is whether the proposed
ZPF-matter interactions generating the phenomenon of mass might involve one or
more resonances. This is presently under investigation.Comment: Revised version of invited presentation at 34th AIAA/ASME/SAE/ASEE
Joint Propulsion Conference, July 13-15, 1998, Cleveland, OH, 10 pages, no
figure
Fannie Hardy Eckstorm Correspondence
Entries include a typed letter from the Office of the Director of the Field Museum of Natural History in Chicago, a request from the Maine State Librarian for help writing a paper, typed and handwritten correspondence between Eckstorm and the Maine State Library some on personal stationery, a typed description of a folk-song collection on the way to the publisher, a call for traditional versions of songs and their airs, Eckstorm\u27s typed biographical sketches of Smyth and Barry, a newspaper review clipping, and a publisher advertisemen
Geometrothermodynamics of black holes
The thermodynamics of black holes is reformulated within the context of the
recently developed formalism of geometrothermodynamics. This reformulation is
shown to be invariant with respect to Legendre transformations, and to allow
several equivalent representations. Legendre invariance allows us to explain a
series of contradictory results known in the literature from the use of
Weinhold's and Ruppeiner's thermodynamic metrics for black holes. For the
Reissner-Nordstr\"om black hole the geometry of the space of equilibrium states
is curved, showing a non trivial thermodynamic interaction, and the curvature
contains information about critical points and phase transitions. On the
contrary, for the Kerr black hole the geometry is flat and does not explain its
phase transition structure.Comment: Revised version, to be published in Gen.Rel.Grav.(Mashhoon's
Festschrift
Schooling for violence and peace : how does peace education differ from ‘normal’ schooling?
This article reviews literature on the roles of schooling in both reproducing and actively perpetrating violence, and sets out an historical explanation of why schools are socially constructed in such a way as to make these roles possible. It then discusses notions of peace education in relation to one particular project in England before using empirical data from research on the project to examine contrasts between peace education approaches and ‘normal’ schooling from the viewpoints of project workers, pupils and teachers. It concludes that such contrasts and tensions do indeed exist and that this raises serious questions about the compatibility of peace education and formal schooling
Mixed States of Composite Fermions Carrying Two and Four Vortices
There now exists preliminary experimental evidence for some fractions, such
as = 4/11 and 5/13, that do not belong to any of the sequences
, and being integers. We propose that these states
are mixed states of composite fermions of different flavors, for example,
composite fermions carrying two and four vortices. We also obtain an estimate
of the lowest-excitation dispersion curve as well as the transport gap; the
gaps for 4/11 are smaller than those for 1/3 by approximately a factor of 50.Comment: Accepted for PRB rapid communication (scheduled to appear in Nov 15,
2000 issue
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