Shifting of the electron-capture-to-the-continuum peak in proton-helium collisions at 10 and 20 keV

A refined theoretical approach has been developed to study the double-differential cross sections (DDCS's) in proton-helium collisions as a function of the ratio of ionized electron velocity to the incident proton velocity. The refinement is done in the present coupled-channel calculation by introducing a continuum distorted wave in the final state coupled with discrete states including direct as well as charge transfer channels. It is confirmed that the electron-capture-to-the-continuum (ECC) peak is slightly shifted to a lower electron velocity than the equivelocity position. Comparing measurements and classical trajectory Monte Carlo (CTMC) calculations at 10 and 20 keV proton energies, excellent agreement of the ECC peak heights is achieved at both energies. However, a minor disagreement in the peak positions between the present calculation and the CTMC results is noted. A smooth behavior of the DDCS is found in the present calculation on both sides of the peak whereas the CTMC results show some oscillatory behavior particularly to the left of the peak, associated with the statistical nature of CTMC calculations.

Polarisation analysis of VUV synchrotron radiation emitted from a bending magnet source in the energy range 20-50 eV: A comparison between measurements and theoretical predictions

The results of a study to characterise the polarisation properties of the photon beam emerging from beamline 5D, mounted on a bending magnet source at the Synchrotron Radiation Source, Daresbury Laboratory, are presented. The expectation values for the Stokes parameters corresponding to the light transmitted by the beamline have been calculated by combining ray-tracing and optical methods. The polarisation of the light at the source is modified both by the beamline geometry and by the reflections at the optical components. Although it is often assumed that the polarising properties of grazing incidence optics are negligible, this assumption leads to rather inaccurate results in the VUV region. A study of the reflectivity shows that even at incidence angles (theta(i) = 80-85degrees) which are far from the Brewster angle (theta(B) similar to 45degrees for VUV and soft X-ray radiation) the residual changes in the amplitudes of the reflected light can result in non-negligible polarisation effects. Furthermore, reflection at grazing incidence gives rise to a substantial change in the phase, and this has the effect of rotating the elliptically polarised state. Theoretical Stokes parameters have been compared with full polarisation measurements obtained using a reflection polarimeter in the energy range 20-40 eV. (C) 2003 Elsevier B.V. All rights reserved.

High-gain x-ray lasing at 11.1 nm in sodiumlike copper driven by a 20-J, 2-ps Nd:glass laser

Evidence of high gain pumped by recombination has been observed in the 5g-4f transition at 11.1 nn in sodiumlike copper ions with use of a 20-J 2-ps Nd:glass laser system. The time- and space-integrated gain coefficient was 8.8 +/- 1.4 cm(-1), indicating a single-transit amplification of similar to 60 times. This experiment has shown that 2 ps is the optimum pulse duration to drive the sodiumlike copper recombination x-ray lasing at 11.1 nm. (C) 1996 Optical Society of America

Energy levels, radiative rates, and electron impact excitation rates for transitions in Li-like ions with 12≤Z≤20

We report calculations of energy levels, radiative rates, and electron impact excitation rates for transitions in Li-like ions with 12≤Z≤20. The grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates, while for determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code is used. Oscillator strengths, radiative rates, and line strengths are reported for all E1, E2, M1, and M2 transitions among the lowest 24 levels of the Li-like ions considered. Collision strengths have been averaged over a Maxwellian velocity distribution, and the effective collision strengths obtained are reported over a wide temperature range up to 10^7.4 K. Additionally, lifetimes are also listed for all calculated levels of the ions. Finally, extensive comparisons are made with results available in the literature, as well as with our parallel calculations for all parameters with the Flexible Atomic Code, in order to assess the accuracy of the reported results. 

Integrated optics for nulling interferometry in the thermal infrared

Modal filtering is based on the capability of single-mode waveguides to transmit only one complex amplitude function to eliminate virtually any perturbation of the interfering wavefronts, thus making very high rejection ratios possible in a nulling interferometer. In the present paper we focus on the progress of Integrated Optics in the thermal infrared [6-20 mu m] range, one of the two candidate technologies for the fabrication of Modal Filters, together with fiber optics. In conclusion of the European Space Agency's (ESA) "Integrated Optics for Darwin" activity, etched layers of clialcogenide material deposited on chalcogenide glass substrates was selected among four candidates as the technology with the best potential to simultaneously meet the filtering efficiency, absolute and spectral transmission, and beam coupling requirements. ESA's new "Integrated Optics" activity started at mid-2007 with the purpose of improving the technology until compliant prototypes can be manufactured and validated, expectedly by the end of 2009. The present paper aims at introducing the project and the components requirements and functions. The selected materials and preliminary designs, as well as the experimental validation logic and test benches are presented. More details are provided on the progress of the main technology: vacuum deposition in the co-evaporation mode and subsequent etching of chalcogenide layers. In addition., preliminary investigations of an alternative technology based on burying a chalcogenide optical fiber core into a chalcogenide substrate are presented. Specific developments of anti-reflective solutions designed for the mitigation of Fresnel losses at the input and output surface of the components are also introduced.

The Value of Adding Optics to Ecosystem Models: A Case Study

Many ecosystem models have been developed to study the ocean's biogeochemical properties, but most of these models use simple formulations to describe light penetration and spectral quality. Here, an optical model is coupled with a previously published ecosystem model that explicitly represents two phytoplankton (picoplankton and diatoms) and two zooplankton functional groups, as well as multiple nutrients and detritus. Surface ocean color fields and subsurface light fields are calculated by coupling the ecosystem model with an optical model that relates biogeochemical standing stocks with inherent optical properties (absorption, scattering); this provides input to a commercially available radiative transfer model (Ecolight). We apply this bio-optical model to the equatorial Pacific upwelling region, and find the model to be capable of reproducing many measured optical properties and key biogeochemical processes in this region. Our model results suggest that non-algal particles largely contribute to the total scattering or attenuation (> 50% at 660 nm) but have a much smaller contribution to particulate absorption (< 20% at 440 nm), while picoplankton dominate the total phytoplankton absorption (> 95% at 440 nm). These results are consistent with the field observations. In order to achieve such good agreement between data and model results, however, key model parameters, for which no field data are available, have to be constrained. Sensitivity analysis of the model results to optical parameters reveals a significant role played by colored dissolved organic matter through its influence on the quantity and quality of the ambient light. Coupling explicit optics to an ecosystem model provides advantages in generating: (1) a more accurate subsurface light-field, which is important for light sensitive biogeochemical processes such as photosynthesis and photo-oxidation, (2) additional constraints on model parameters that help to reduce uncertainties in ecosystem model simulations, and (3) model output which is comparable to basic remotely-sensed properties. In addition, the coupling of biogeochemical models and optics paves the road for future assimilation of ocean color and in-situ measured optical properties into the models.

Primary optics for efficient high-brightness LED color mixing

In SSL general illumination, there is a clear trend to high flux packages with higher efficiency and higher CRI addressed with the use of multiple color chips and phosphors. However, such light sources require the optics provide color mixing, both in the near-field and far-field. This design problem is specially challenging for collimated luminaries, in which diffusers (which dramatically reduce the brightness) cannot be applied without enlarging the exit aperture too much. In this work we present first injection molded prototypes of a novel primary shell-shaped optics that have microlenses on both sides to provide Köhler integration. This shell is design so when it is placed on top of an inhomogeneous multichip Lambertian LED, creates a highly homogeneous virtual source (i.e, spatially and angularly mixed), also Lambertian, which is located in the same position with only small increment of the size (about 10-20%, so the average brightness is similar to the brightness of the source). This shell-mixer device is very versatile and permits now to use a lens or a reflector secondary optics to collimate the light as desired, without color separation effects. Experimental measurements have shown optical efficiency of the shell of 95%, and highly homogeneous angular intensity distribution of collimated beams, in good agreement with the ray-tracing simulations.

Innovative education networking aimed at multimedia tools for geometrical optics learning

We present a purposeful initiative to open new grounds for teaching Geometrical Optics. It is based on the creation of an innovative education networking involving academic staff from three Spanish universities linked together around Optics. Nowadays, students demand online resources such as innovative multimedia tools for complementing the understanding of their studies. Geometrical Optics relies on basics of light phenomena like reflection and refraction and the use of simple optical elements such as mirrors, prisms, lenses, and fibers. The mathematical treatment is simple and the equations are not too complicated. But from our long time experience in teaching to undergraduate students, we realize that important concepts are missed by these students because they do not work ray tracing as they should do. Moreover, Geometrical Optics laboratory is crucial by providing many short Optics experiments and thus stimulating students interest in the study of such a topic. Multimedia applications help teachers to cover those student demands. In that sense, our educational networking shares and develops online materials based on 1) video-tutorials of laboratory experiences and of ray tracing exercises, 2) different online platforms for student self-examinations and 3) computer assisted geometrical optics exercises. That will result in interesting educational synergies and promote student autonomy for learning Optics.

Absolute photometry of the light of the night sky ; the zenith intensity of Haleakala (latitude N 20.7 degrees) and at Fritz Peak (latitude N 39.9 degrees) /

Includes bibliography.