Claire E. Max

The W. M. Keck Observatory Laser Guide Star Adaptive Optics System: Overview

The Keck Observatory began science observations with a laser guide star adaptive optics system, the first such system on an 8-10 m class telescope, in late 2004. This new capability greatly extends the scientific potential of the Keck II Telescope, allowing near-diffraction-limited observations in the near-infrared using natural guide stars as faint as 19th magnitude. This paper describes the conceptual approach and technical implementation followed for this system, including lessons learned, and provides an overview of the early science capabilities.

First Light Adaptive Optics Images from the Keck II Telescope : A New Era of High Angular Resolution Imagery

ABSTRACT Adaptive optics (AO) is a technology that corrects in real time for the blurring effects of atmospheric turbulence, in principle allowing Earth‐bound telescopes to achieve their diffraction limit and to “see” as clearly as if they were in space. The power of AO using natural guide stars has been amply demonstrated in recent years on telescopes up to 3–4 m in diameter. The next breakthrough in astronomical resolution was expected to occur with the implementation of AO on the new generation of large, 8–10 m diameter telescopes. In this paper we report the initial results from the first of these AO systems, now coming on line on the 10 m diameter Keck II Telescope. The results include the highest angular resolution images ever obtained from a single telescope (0 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsx...

Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager

An exoplanet extracted from the bright Direct imaging of Jupiter-like exoplanets around young stars provides a glimpse into how our solar system formed. The brightness of young stars requires the use of next-generation devices such as the Gemini Planet Imager (GPI). Using the GPI, Macintosh et al. discovered a Jupiter-like planet orbiting a young star, 51 Eridani (see the Perspective by Mawet). The planet, 51 Eri b, has a methane signature and is probably the smallest exoplanet that has been directly imaged. These findings open the door to understanding solar system origins and herald the dawn of a new era in next-generation planetary imaging. Science, this issue p. 64; see also p. 39 The Gemini Planet Imager detects a Jupiter-like exoplanet orbiting the young star 51 Eridani. [Also see Perspective by Mawet] Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10−6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, “hot-start” formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the “cold-start” core-accretion process that may have formed Jupiter.

Strong self‐focusing due to the ponderomotive force in plasmas

Self‐focusing of cylindrical beams due to the ponderomotive force behaves quite differently for the full exponential nonlinearity than for the weak, cubic‐nonlinearity limit. Steady self‐trapped propagation becomes possible for arbitrary incident powers. Self‐focusing becomes a periodic oscillatory phenomenon, rather than a catastrophic process in which the light intensity increases without limit.

A model for laser driven ablative implosions

A theoretical model is presented describing the spatial structure and scaling laws of laser driven ablative implosions. The effect of inhibited electron thermal transport is explicitly included. The theory is in excellent agreement with results from a computer hydrodynamics code, under conditions when heat flow is flux‐limited at the critical surface and suprathermal electrons do not form a dominant energy transport mechanism.

Planar laser‐driven ablation: Effect of inhibited electron thermal conduction

A model for planar laser‐driven ablation is presented, including the effects of inhibited electron thermal conduction. Localized deposition of laser energy at the critical‐density surface is assumed. A steady‐state solution in the conduction zone is joined to a rarefaction wave in the underdense corona. The global flow structure is calculated, as well as the ablation pressure, ablation rate, and hydrodynamic efficiency. Criteria are developed for the importance of the inertial force caused by the acceleration of the slab. The results agree well with time‐dependent computer simulations using a Lagrangian hydrodynamics code.

Relativistic, perpendicular shocks in electron-positron plasmas

One-dimensional particle-in-cell plasma simulations are used to examine the mechanical structure and thermalization properties of collisionless relativistic shock waves in electron-positron plasmas. Shocks propagating perpendicularly to the magnetic field direction are considered. It is shown that these shock waves exist, and that they are completely parameterized by the ratio of the upstream Poynting flux to the upstream kinetic energy flux. The way in which the Rankine-Hugoniot shock jump conditions are modified by the presence of wave fluctuations is shown, and they are used to provide a macroscopic description of these collisionless shock flows. The results of a 2D simulation that demonstrates the generality of these results beyond the assumption of the 1D case are discussed. It is suggested that the thermalization mechanism is the formation of a synchrotron maser by the coherently reflected particles in the shock front. Because the downstream medium is thermalized, it is argued that perpendicular shocks in pure electron-positron plasmas are not candidates as nonthermal particle accelerators. 40 refs.

Laser irradiation of disk targets at 0.53 μm wavelength

Results and analyses are presented for laser irradiation of Be‐, CH‐, Ti‐, and Au‐disk targets with 0.53 μm light in 3–200 J, 600–700 psec pulses, at nominal incident intensities from 3×1013 to 5×1015 W/cm2. The measured absorptions are higher than observed in similar 1.06 μm irradiations, and are largely consistent with modeling which shows the importance of inverse‐bremsstrahlung and Brillouin scattering. Observed red‐shifted back‐reflected light shows that Brillouin scattering occurs at low to moderate levels. Backscattering fractions up to 30% were observed in the f/2 focusing lens. The measured fluxes of multi‐keV x rays indicate hot‐electron fractions of 1% or less, with temperatures of 6 to 20 keV which are consistent with resonance absorption or perhaps 2ωpe. Measurements show 30%–50% efficient conversion of absorbed light into sub‐keV x rays, with time‐, angular‐, and spatial‐emission distributions which are generally consistent with non‐local‐thermodynamic‐equilibrium modeling using inhibited th...

Enhanced transport across laser generated magnetic fields

Laser generated mega‐Gauss magnetic fields may have a disordered small‐scale structure, because many different field generation mechanisms are operating simultaneously. Electron cross‐field transport in such fields is studied, concentrating on three specific nonclassical transport processes: resonant scattering, field line wandering, and an analog of neoclassical diffusion. Each of these mechanisms seems capable of producing cross‐field transport rates significantly faster than the classical values for a mega‐Gauss magnetic field, yet considerably slower than the classical value for a field‐free plasma.

Stimulated scattering of light by ion modes in a homogeneous plasma: Space-time evolution

Stimulated Brillouin scattering, filamentation, and induced Thomson scattering are studied for a coherent electromagnetic plane wave propagating in a uniform plasma. A generalized Green’s function is found that describes the impulse response for stimulated scattering by electron and ion modes. Explicit asymptotic Green’s functions are calculated for those parametric instabilities involving ion modes or quasi‐modes. Special attention is given to whether the instabilities are convective or absolute. For a traveling wave pump in a uniform plasma, Brillouin and induced Thomson backscatter can be absolute, but sidescatter is convective; filamentation of traveling waves is always convective. Spatial growth rates are calculated for convectively unstable modes. Finally, the competition of filamentation and stimulated Brillouin scattering is considered for parameters typical of real laser‐fusion experiments.