On the cometary hydrogen coma and far UV emission

Cometary hydrogen observations are reviewed with emphasis on observations of comet Bennett. The results are theoretically interpreted and a brief summary of ultraviolet observations other than Lyman alpha is given

Polarimetry from the Ground Up

Ground-based solar polarimetry has made great progress over the last decade. Nevertheless, polarimetry is still an afterthought in most telescope and instrument designs, and most polarimeters are designed based on experience and rules of thumb rather than using more formal systems engineering approaches as is common in standard optical design efforts. Here we present the first steps in creating a set of systems engineering approaches to the design of polarimeters that makes sure that the final telescope-instrument-polarimeter system is more than the sum of its parts.Comment: To appear in proceedings of the Solar Polarization Workshop

Dynamical mean-field theory for the normal phase of the attractive Hubbard model

We analyze the normal phase of the attractive Hubbard model within dynamical mean-field-theory. We present results for the pair-density, the spin-susceptibility, the specific heat, the momentum distribution, and for the quasiparticle weight. At weak coupling the low-temperature behavior of all quantities is consistent with Fermi liquid theory. At strong coupling all electrons are bound pairs, which leads to a spin gap and removes fermionic quasi-particle excitations. The transition between the Fermi liquid phase and the pair phase takes place at a critical coupling of the order of the band-width and is generally discontinuous at sufficiently low temperatures

Electroweak Radiative Corrections to WW and ZZ Boson Production in Hadronic Collisions

Some results of a calculation of electroweak radiative corrections to $W$ and $Z$ boson production in hadronic collisions are presented.Comment: 4 pages, LaTeX, uses sprocl.sty, 2 embedded postscript figures, to appear in the Proceedings of the DPF96 Conferenc

Polarization properties of real aluminum mirrors; I. Influence of the aluminum oxide layer

In polarimetry it is important to characterize the polarization properties of the instrument itself to disentangle real astrophysical signals from instrumental effects. This article deals with the accurate measurement and modeling of the polarization properties of real aluminum mirrors, as used in astronomical telescopes. Main goals are the characterization of the aluminum oxide layer thickness at different times after evaporation and its influence on the polarization properties of the mirror. The full polarization properties of an aluminum mirror are measured with Mueller matrix ellipsometry at different incidence angles and wavelengths. The best fit of theoretical Mueller matrices to all measurements simultaneously is obtained by taking into account a model of bulk aluminum with a thin aluminum oxide film on top of it. Full Mueller matrix measurements of a mirror are obtained with an absolute accuracy of ~1% after calibration. The determined layer thicknesses indicate logarithmic growth in the first few hours after evaporation, but it remains stable at a value of 4.12+/-0.08 nm on the long term. Although the aluminum oxide layer is established to be thin, it is necessary to consider it to accurately describe the mirror's polarization properties.Comment: accepted for publication in PAS

Ultrafast solid-state laser oscillators: a success story for the last 20years with no end in sight

Ultrashort lasers provide an important tool to probe the dynamics of physical systems at very short time-scales, allowing for improved understanding of the performance of many devices and phenomena used in science, technology, and medicine. In addition ultrashort pulses also provide a high peak intensity and a broad optical spectrum, which opens even more applications such as material processing, nonlinear optics, attosecond science, and metrology. There has been a long-standing, ongoing effort in the field to reduce the pulse duration and increase the power of these lasers to continue to empower existing and new applications. After 1990, new techniques such as semiconductor saturable absorber mirrors (SESAMs) and Kerr-lens mode locking (KLM) allowed for the generation of stable pulse trains from diode-pumped solid-state lasers for the first time, and enabled the performance of such lasers to improve by several orders of magnitude with regards to pulse duration, pulse energy and pulse repetition rates. This invited review article gives a broad overview and includes some personal accounts of the key events during the last 20 years, which made ultrafast solid-state lasers a success story. Ultrafast Ti:sapphire, diode-pumped solid-state, and novel semiconductor laser oscillators will be reviewed. The perspective for the near future indicates continued significant progress in the fiel

Modeling of the Terminal Velocities of the Dust Ejected Material by the Impact

We compute the distribution of velocities of the particles ejected by the impact of the projectile released from NASA Deep Impact spacecraft on the nucleus of comet 9P/Tempel 1 on the successive 20 hours following the collision. This is performed by the development and use of an ill-conditioned inverse problem approach, whose main ingredients are a set of observations taken by the Narrow Angle Camera (NAC) of OSIRIS onboard the Rosetta spacecraft, and a set of simple models of the expansion of the dust ejecta plume for different velocities. Terminal velocities are derived using a maximum likelihood estimator. We compare our results with published estimates of the expansion velocity of the dust cloud. Our approach and models reproduce well the velocity distribution of the ejected particles. We consider these successful comparisons of the velocities as an evidence for the appropriateness of the approach. This analysis provides a more thorough understanding of the properties of the Deep Impact dust cloud.Comment: Comments: 6 pages, 2 Postscript figures, To appear in the proceedings of "Deep Impact as a World Observatory Event - Synergies in Space, Time", ed. Hans Ulrich Kaeufl and Chris Sterken, Springer-Verla