This paper describes the design and fabrication of a range of ‘gas cell’ microtargets produced by the Target Fabrication Group in the Central Laser Facility (CLF) for academic access experiments on the Orion laser facility at the Atomic Weapons Establishment (AWE). The experiments were carried out by an academic consortium led by Imperial College London. The underlying target methodology was an evolution of a range of targets used for experiments on radiative shocks and involved the fabrication of a precision machined cell containing a number of apertures for interaction foils or diagnostic windows. The interior of the cell was gas-filled before laser irradiation. This paper details the assembly processes, thin film requirements and micro-machining processes needed to produce the targets. Also described is the implementation of a gas-fill system to produce targets that are filled to a pressure of 0.1–1 bar. The paper discusses the challenges that are posed by such a target.

This work considers debris disks whose spectra can be modelled by dust emission at two different temperatures. These disks are typically assumed to be a sign of multiple belts, but only a few cases have been confirmed via high resolution observations. We derive the properties of a sample of two-temperature disks, and explore whether this emission can arise from dust in a single narrow belt. While some two-temperature disks arise from single belts, it is probable that most have multiple spatial components. These disks are plausibly similar to the outer Solar System's configuration of Asteroid and Edgeworth-Kuiper belts separated by giant planets. Alternatively, the inner component could arise from inward scattering of material from the outer belt, again due to intervening planets. For either scenario, the ratio of warm/cool component temperatures is indicative of the scale of outer planetary systems, which typically span a factor of about ten in radius.

This article describes the fabrication of a suite of laser targets by the Target Fabrication group in the Central Laser Facility (CLF), STFC Rutherford Appleton Laboratory for the first academic-access experiment on the Orion laser facility (Hopps et al., Appl. Opt. 52, 3597–3601 (2013)) at Atomic Weapons Establishment (AWE). This experiment, part of the POLAR project (Falize et al., Astrophys. Space Sci. 336, 81–85 (2011); Busschaert et al., New J. Phys. 15, 035020 (2013)), studied conditions relevant to the radiation-hydrodynamic processes occurring in a remarkable class of astrophysical star systems known as magnetic cataclysmic variables. A large number of complex fabrication technologies and research and development activities were required to field a total of 80 high-specification targets. Target design and fabrication procedures are described and initial alignment and characterization data are discussed.

Colloids with anisotropic shape and properties can enable the assembly of advanced materials otherwise not attainable by microfabrication. In this study, we present a convenient method using common microfabrication tools to generate a diverse array of non-spherical microparticles with well-defined shapes, sizes, electromagnetic properties for self-assembly applications. Projection photolithography onto SU-8 photoresist enabled the production of large aspect ratio microparticles such as cubes, cuboids, cylinders, hexagonal prisms, and parallelepipeds. We characterized these particles to confirm their anisotropic shape and size monodispersity. Fluorescent stains (e.g., Nile red) were mixed into the photoresist prepolymer to enhance the visualization of particle orientation. Particles designed for passive self-assembly were prepared by conventional photolithographic techniques. Particles designed for active assembly were then decorated with metallic patches in precise locations along the surface (e.g., top, side or multiple sides) using electron beam metal evaporation. This metal deposition process can enable orientational control of particles during their assembly in directed fields. After fabrication, large particles (e.g., 1,000 µm3) were released from the substrate via gentle sheer forces, whereas small particles (e.g., 10 µm3) were released by the dissolution of a sacrificial layer underneath the SU-8. Suspending the particles in water with surfactant (or other suitable solvents) provided amenable conditions for their assembly in static or dynamic systems. These conventional methods have the potential to catalyze new research in the fabrication and assembly of anisotropic patchy particles with controllable properties for the hierarchical development of self-assembled micromirrors, biosensors, and photonic crystals as examples.

Whilst debris discs orbiting main-sequence stars are well studied, very little is known regarding their fate when the star evolves onto the giant branch. For intermediate mass (A-type) stars, giants provide a unique opportunity to detect planets using the radial velocity technique, otherwise prohibited by high jitter levels and rotationally broadened lines in main-sequence intermediate mass (A-type) stars. Such stars can provide key insights into the structure of planetary systems around intermediate mass stars. In our Herschel OT1 program (PI Bonsor) we searched for the presence of debris discs orbiting a sample of 36 subgiants, half of which have RV detected companions. Our best detection is the resolved debris disc orbiting κ CrB.

This contribution summarises the first characterisation of the 12 μm warm dust (“exo-Zodi”) luminosity function around Sun-like stars, focussing on the dustiest systems that can be identified by the WISE mission (Kennedy & Wyatt 2013). We use the sample of main-sequence stars observed by Hipparcos within 150pc as an unbiased sample, and report the detection of six new warm dust candidates. The ages of five of these new sources are unknown, meaning that they may be sites of terrestrial planet formation or rare analogues of other old warm dust systems. We show that the dustiest old (> Gyr) systems such as BD+20 307 are 1 in 10,000 occurrences. Bright warm dust is much more common around young (<120 Myr) systems, with a ~1% occurrence rate. We show that a two component in situ model where all stars have initially massive warm disks and in which warm debris is also generated at some random time along the stars' main-sequence lifetime, perhaps due to a collision, can explain the observations. However, if all stars only have initially massive warm disks these would not be visible at Gyr ages, and random collisions on the main-sequence are too infrequent to explain the high disk occurrence rate for young stars. That is, neither component can explain the observations on their own. Despite these conclusions, we cannot rule out an alternative dynamical model in which comets are scattered in from outer regions because the distribution of systems with the appropriate dynamics is unknown. Our in situ model predicts that the fraction of stars with exo-Zodi bright enough to cause problems for future exo-Earth imaging attempts is at least roughly 10%, and is higher for populations of stars younger than a few Gyr. This prediction of roughly 10% also applies to old stars because bright systems like BD+20 307 imply a population of fainter systems that were once bright, but are now decaying through fainter levels. Our prediction should be strongly tested by the Large Binocular Telescope Interferometer, which will provide valuable constraints and input for more detailed evolution models. A detection fraction lower than our prediction could indicate that the hot dust in systems like BD+20 307 has a cometary origin due to the quirks of the planetary dynamics. Population models of comet delivery need to be developed to help distinguish between different possible origins of warm dust.

The eccentric orbits of the known extrasolar giant planets provide evidence that most planet-forming environments undergo violent dynamical instabilities. Here, we numerically simulate the impact of giant planet instabilities on planetary systems as a whole. We find that populations of inner rocky and outer icy bodies are both shaped by the giant planet dynamics and are naturally correlated. Strong instabilities – those with very eccentric surviving giant planets – completely clear out their inner and outer regions. In contrast, systems with stable or low-mass giant planets form terrestrial planets in their inner regions and outer icy bodies produce dust that is observable as debris disks at mid-infrared wavelengths. Fifteen to twenty percent of old stars are observed to have bright debris disks (at λ ~ 70μm) and we predict that these signpost dynamically calm environments that should contain terrestrial planets.

The planetary system of HD 69830 is uniquely constrained by observations of (i) an infrared excess indicative of a debris disk with warm dust and (ii) radial velocity variations indicative of three planets. This presents a valuable opportunity to test planet formation models by integrating dynamical models of planetary formation and migration with those for the sculpting of a dust-producing planetesimal disk. We perform n-body simulations and investigate the excitation of both planet and planetesimal eccentricities, the accretion of planetesimals onto the planets, and the clearing of a planetesimal disk by the planets as they grow in mass and migrate through the disk. In simulations tuned to closely follow previous semi-analytic models for the growth and migration of the planets, we find that the inner planet accretes significantly more planetesimals than previously estimated. We find that eccentricity excitation due to mutual planetary perturbations during and after the migration do not naturally produce the observed eccentricities. Our simulations suggest that this discrepancy may be reduced or possibly reconciled if the planets are significantly more massive than expected (possible if the planetary system's angular momentum were nearly parallel to our line of sight). Even if the planets are significantly more massive than previously assumed, we find that the migrating planets are inefficient at clearing the outer planetesimal disk and that a significant fraction of the planetesimal population beyond 1 AU remains bound on moderately eccentric and inclined orbits. While much of the remaining planetesimal belt would have eroded via a collisional cascade and radiation pressure, we explore whether some of the highly excited planetesimals may be able to persist over the age of the central star, producing the dust observed in the HD 69830 system.

Polycrystalline Cd1-xMgxTe (CMT) thin films are a potential absorber material for two-junction thin-film tandem solar cell applications because the desired top cell bandgap range of 1.6 to 1.8 eV is readily obtained using CMT with only small resultant changes in the lattice constant from that of CdTe. Tandem devices require the top cell to have a transparent back contact to transmit the sub-bandgap spectrum to the bottom cell. Sputtered Cu-doped ZnTe (ZnTe:Cu) thin films, which offer potential as a transparent back contact interface layer, have been used successfully in CdTe devices. We apply ZnTe:Cu back contacts to CMT devices to continue development toward a transparent top cell. We describe the effects of depositing ZnTe:Cu at different temperatures and with different Cu contents on the net acceptor concentration, minority carrier lifetime, and device performance. We present here the highest reported CMT device efficiency of 9.6% at a bandgap of 1.57 eV.

Several wet-processing steps are used in fabricating high-efficiency CdTe/CdS solar cells. These steps can hinder in-line processing; thus, developing an all-dry processing option is attractive for a manufacturing-friendly process. In this study, we systematically modified the baseline process used in our laboratory to replace CdS deposited by chemical-bath deposition (CBD) with sputter-deposited CdS and Cu-doped graphite paste back-contact with Cu-doped ZnTe deposited by radio-frequency sputtering. In addition to CdTe deposited by close-spaced sublimation, we also used conventionally evaporated CdTe. The results show that replacing only CBD CdS with oxygenated CdS deposited by sputtering produces devices with performance comparable to baseline devices if the front bilayer SnO2 is replaced by a Cd2SnO4/ZnSnO alloy. Replacing the graphite paste back-contact with sputter-deposited Cu-doped ZnTe resulted in device performance comparable to baseline devices. Incorporating both dry processing steps gave performance comparable to the devices with sputtered CdS with a SnO2 front contact. We used capacitance-voltage and minority-carrier lifetime measurements to analyze the factors affecting device performance and we present the results here.