The Whole is Greater than the Sum of the Parts: Optimizing the Joint Science Return from LSST, Euclid and WFIRST

The focus of this report is on the opportunities enabled by the combination of LSST, Euclid and WFIRST, the optical surveys that will be an essential part of the next decade's astronomy. The sum of these surveys has the potential to be significantly greater than the contributions of the individual parts. As is detailed in this report, the combination of these surveys should give us multi-wavelength high-resolution images of galaxies and broadband data covering much of the stellar energy spectrum. These stellar and galactic data have the potential of yielding new insights into topics ranging from the formation history of the Milky Way to the mass of the neutrino. However, enabling the astronomy community to fully exploit this multi-instrument data set is a challenging technical task: for much of the science, we will need to combine the photometry across multiple wavelengths with varying spectral and spatial resolution. We identify some of the key science enabled by the combined surveys and the key technical challenges in achieving the synergies.Comment: Whitepaper developed at June 2014 U. Penn Workshop; 28 pages, 3 figure

Exploring the NRO Opportunity for a Hubble-sized Wide-field Near-IR Space Telescope -- NEW WFIRST

We discuss scientific, technical and programmatic issues related to the use of an NRO 2.4m telescope for the WFIRST initiative of the 2010 Decadal Survey. We show that this implementation of WFIRST, which we call "NEW WFIRST," would achieve the goals of the NWNH Decadal Survey for the WFIRST core programs of Dark Energy and Microlensing Planet Finding, with the crucial benefit of deeper and/or wider near-IR surveys for GO science and a potentially Hubble-like Guest Observer program. NEW WFIRST could also include a coronagraphic imager for direct detection of dust disks and planets around neighboring stars, a high-priority science and technology precursor for future ambitious programs to image Earth-like planets around neighboring stars.Comment: 76 pages, 26 figures -- associated with the Princeton "New Telescope Meeting

Transforms for intra prediction residuals based on prediction inaccuracy modeling

In intra video coding and image coding, the directional intra prediction is used to reduce spatial redundancy. Intra prediction residuals are encoded with transforms. In this paper, we develop transforms for directional intra prediction residuals. Specifically, we observe that the directional intra prediction is most effective in smooth regions and edges with a particular direction. In the ideal case, edges can be predicted fairly accurately with an accurate prediction direction. In practice, an accurate prediction direction is hard to obtain. Based on the inaccuracy of prediction direction that arises in the design of many practical video coding systems, we can estimate the residual variance and propose a class of transforms based on the estimated variance function. The proposed method is evaluated by the energy compaction property. Experimental results show that with the proposed method, the same amount of energy in directional intra prediction residuals can be preserved with a significantly smaller number of transform coefficients

The assessment of visual behaviour and depth perception in surgery

Imperial Users onl

Structuring high-order harmonic generation with the angular momentum of light

Tesis por compendio de publicaciones[ES] Los pulsos láser ultracortos son una herramienta única para explorar las dinámicas más rápidas de la materia. Sorprendentemente, los pulsos de láser más cortos obtenidos hasta la fecha se producen a partir del fenómeno no lineal de conversión de frecuencias de generación de armónicos de orden alto (HHG), que resulta en la emisión de pulsos con duraciones de attosegundo. Es importante destacar que estos pulsos de attosegundo pueden exhibir una propiedad muy interesante, el momento angular, que presenta dos formas diferentes, el momento angular de espín (SAM) y el momento angular orbital (OAM), y que abre nuevos escenarios para las interacciones luz-materia a escalas espaciales nanométricas y temporales ultracortas. En esta tesis desarrollamos un conjunto de esquemas para la crea- ción de armónicos de orden alto y pulsos de attosegundo con nuevas propiedades de momento angular mediante la estructuración del pro- ceso de HHG a través de las características de los haces incidentes. Para ese propósito, primero abordamos la descripción de los mecanismos físicos fundamentales de la HHG. En particular, estudiamos la ioniza- ción túnel en moléculas, descubriendo que depende de la ubicación del electrón dentro de la molécula, debido a la naturaleza extendida de estas. Esta característica deja huellas importantes en los espectros de HHG y de fotoelectrones. Por lo tanto, hemos desarrollado una receta para implementar este fenómeno en los modelos de campos intensos existentes. A continuación, predecimos y describimos teóricamente la gene- ración de haces láser en el ultravioleta extremo (XUV) con nuevas propiedades de momento angular que, en la mayoría de los casos, son también creadas y caracterizadas experimentalmente por nuestros colaboradores del grupo Kapteyn-Murnane en JILA, en la Universidad de Colorado (EE. UU.), y del grupo del Prof. M.-Ch. Chen del Instituto de Tecnologías Fotónicas de la Universidad Tsing Hua (Taiwán). Para empezar, demostramos la generación, por primera vez, de haces de luz con OAM variable en el tiempo, una propiedad que denominamos como el auto-torque de la luz. Es importante destacar que los haces con auto-torque surgen naturalmente en el régimen XUV cuando el campo incidente para la HHG está formado por dos vórtices infrarro- jos retardados en el tiempo. Bajo esta configuración, el OAM de los armónicos de orden alto cambia a lo largo del tiempo en una escala de tiempo de attosegundos, siendo la cantidad de auto-torque controlada a través de las propiedades temporales de los pulsos incidentes. Por lo tanto, creemos que los haces con auto-torque pueden servir como nuevas herramientas para la manipulación láser-materia. Además, mostramos cómo el OAM puede servir como instrumento para mani- pular las propiedades espectrales y de divergencia de los armónicos de orden alto. Empleando dos vórtices con el contenido adecuado de OAM como pulsos incidentes, obtenemos peines de frecuencias de armónicos de orden alto con un espaciado entre líneas espectrales sintonizable y baja divergencia. Este control es particularmente intere- sante para espectroscopía y formación de imagen en el XUV o incluso en los rayos X blandos. Además, presentamos varios esquemas para el control de la eliptici- dad de los pulsos de attosegundo y de los armónicos de orden alto. Utilizando la configuración no colineal contrarrotante, extraemos el escalado de la elipticidad de los armónicos de orden alto con la de los haces incidentes y desvelamos la información sobre la respuesta dipolar oculta en esa conexión. Además, mostramos la generación de vórtices polarizados circularmente a partir de la HHG usando un campo incidente bi-circular vorticial. Destacablemente, al seleccionar correctamente el OAM del campo incidente, podemos obtener, o bien pulsos de attosegundo polarizados circularmente, o bien armónicos de orden alto con baja carga topológica. Por último, demostramos teóricamente la generación de trenes de pulsos de attosegundo con estados de polarización ordenados temporalmente mediante la combi- nación de dos campos incidentes bi-circulares vorticiales retardados en el tiempo. Creemos que la generación de pulsos de attosegundo con elipticidad controlada se puede emplear para el estudio de la dinámica ultrarrápida de SAM en moléculas quirales o materiales magnéticos. [EN] Ultrashort laser pulses are a unique tool to explore the fastest dy- namics in matter. Remarkably, the shortest laser pulses to date are produced from the non-linear frequency upconversion phenomenon of high-order harmonic generation (HHG), which results in the emis- sion of pulses of attosecond durations. Importantly, such attosecond pulses can exhibit a very exciting property, the angular momentum, which presents two different forms, the spin angular momentum (SAM) and the orbital angular momentum (OAM), and that brings new sce- narios for the light-matter interactions at the nanometric spatial and ultrashort temporal scales. In this thesis work, we develop a compilation of schemes for the creation of high-order harmonics and attosecond pulses with novel angular momentum properties by structuring the HHG process through the characteristics of the driving beams. For that purpose, we first address the description of the fundamental physical mechanisms of HHG. In particular, we study the tunnel ionization in molecules, finding that it is site-specific—its rate depends on the position of the electronic wavefunction at the ion sites—, due to the extended nature of the molecules. This characteristic leaves important signatures in the HHG and photoelectron spectra. Therefore, we provide a recipe for implementing the site-specificity in the existing strong-field models. Afterwards, we theoretically predict and describe the creation of extreme-ultraviolet (XUV) beams with novel angular momentum prop- erties, which, in most of the cases, are experimentally generated and characterized by our collaborators from the Kapteyn-Murnane group in JILA, at the University of Colorado (USA) and from the group of Prof. M.-Ch. Chen at the Institute of Photonics Technologies of the Tsing Hua University (Taiwan). To begin with, we demonstrate the generation, for the first time, of light beams with time-varying OAM, a property which we denote as the self-torque of light. Importantly, self- torqued beams arise naturally in the XUV regime from HHG driven by two time-delayed infrared vortex beams. Under this configuration, the OAM of the high-order harmonics changes along time in the attosec- ond time-scale, being the amount of self-torque controlled through the temporal properties of the driving pulses. Thus, we believe that self-torqued beams can serve as unprecedented tools for laser-matter manipulation. In addition, we show how the OAM can serve as an instrument to manipulate the spectral and divergence properties of the high-order harmonics. By driving HHG with two vortex beams with properly selected OAM, we obtain high-order harmonic frequency combs with tunable line-spacing and low divergence. Such control is particularly interesting for XUV/soft-X-ray spectroscopy and imaging. Moreover, we present several schemes for the ellipticity control of the high-order harmonics and attosecond pulses. Using the non-collinear counter-rotating scheme, we extract the scaling of the ellipticity of the high-order harmonics with that of the driving beams’ and we unveil the information about the non-perturbative dipole response hidden in that connection. Also, we show the generation of circularly polarized vortex beams from HHG driven by a bi-circular vortex field. Interest- ingly, by properly selecting the OAM of the driving field we can obtain either circularly polarized attosecond pulses, or high-order harmonics with low topological charge. Finally, we theoretically demonstrate the generation of attosecond pulse trains with time-ordered polarization states by combining two time-delayed bi-circular vortex driving fields. We believe that the generation of attosecond pulses with controlled ellipticity can be employed for the study of ultrafast spin dynamics in chiral molecules or magnetic materials