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 $\nu$ = 4/11 and 5/13, that do not belong to any of the sequences $\nu=n/(2pn\pm 1)$, $p$ and $n$ 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