Wetted-foam layers are of significant interest for inertial-confinement-fusion capsules, due to the control they provide over the convergence ratio of the implosion and the opportunity this affords to minimize hydrodynamic instability growth. However, the equation of state for fusion-relevant foams are not well characterized, and many simulations rely on modeling such foams as a homogeneous medium with the foam average density. To address this issue, an experiment was performed using the VULCAN Nd:glass laser at the Central Laser Facility. The aim was to measure the principal Hugoniot of TMPTA plastic foams at 260mg/cm^{3}, corresponding to the density of liquid DT-wetted-foam layers, and their "hydrodynamic equivalent" capsules. A VISAR was used to obtain the shock velocity of both the foam and an α-quartz reference layer, while streaked optical pyrometry provided the temperature of the shocked material. The measurements confirm that, for the 20-120 GPa pressure range accessed, this material can indeed be well described using the equation of state of the homogeneous medium at the foam density.

The interaction of very intense and ultrashort laser pulses with solid targets is a topic that has attracted a large amount of interest in science and applications. This interest is boosted by the large progress made in the development of high repetition rate, high-power laser systems. With the significant increase in average power, there is concern about how to deal with ablated debris that may lead to contamination and damage during interaction experiments with solid targets. This issue is also highly relevant in experiments that include plasma mirrors. These are often employed to increase the contrast ratio of the intense laser pulse to unwanted laser pre-pulses from the amplifier chain and/or the background of amplified spontaneous emission. For this reason, the present work investigates the mass ejected from the target into vacuum for different conditions, particularly those present when plasma mirrors are introduced. The total amount of ablated mass can be reduced by making use of a temporally controlled plasma expansion that enhances the plasma mirror reflectivity. In this way, high intensity laser interaction experiments can be carried out with efficient and clean plasma mirrors significantly reducing the degradation of the laser optics and plasma diagnostics placed near the interaction.

900 nanometre thick aluminium strips were produced by the Target Fabrication Group for an experiment at the Central Laser Facility. They were specified to be supported horizontally at either end across an 800 micron void and to be 500 microns in height. The production method used a Parylene (C8H8) supporting layer which was removed by oxygen plasma etching. This process resulted in a problematic contaminant layer that caused substantial increase to the absorption of X-rays in the laser campaign. The contaminant layer was characterised by optical microscopy and Scanning Electron Microscopy. Energy Dispersive X-ray Spectroscopy was able to detect a high relative abundance of carbon and oxygen in the plastic etched strips when compared to control samples. It has been shown that partially etched Parylene can form carboxylic groups with a ratio of 4:1 carbon to oxygen atoms. This effect was observed and exacerbated by the sample geometry not in sufficient contact with the grounded chamber baseplate causing charging and therefore insufficient hydrogen abstraction in the plasma. An alternative production method produced strips that were not as flat over the open area as the previous method but had no significant contaminant layer. This process involved coating a release layer of sodium chloride before the aluminium strips. When lowered into water, the salt dissolves in water and the strips are suspended on the surface tension, allowing the strips to be picked onto the mount. Each target required measuring for form using a white light interferometer where around half were within specification.

Surface roughness scans of NaCl (salt) coatings on silicon wafers were carried out using an Atomic Force Microscope. Metrology was carried out on single layer salt and also salt coated with a thin aluminium layer which is a representative high power laser target. All were characterised straight from vacuum and again after being exposed to the atmosphere for a few days. Results suggest that the surface roughness increased drastically after being left in atmospheric conditions for few days. The roughness increased by almost five time for an exposed salt coating. For a salt coating with an aluminium layer the roughness only increased slightly (similar to 1nm). This suggests that it's important to coat materials for the laser target on to salt release layers almost immediately from vacuum. This work enables production processes and quality control for high power laser targets to be defined and an understanding of possible pinhole production in thin film coatings.

It is widely understood within the high-power laser community that recent developments in diode pumped and high repetition rate laser systems will give unprecedented access to laser shots. This will provide a challenge for target fabrication in making enough experimental samples. While in the past access to facilities and shot rates during access periods have been the limiting factor for high power laser experiments this will soon not be the case. There has already been a shift in development of the user base from fundamental science experiments to industrial applications using the laser experiment as a reliable source for secondary aims. The Astra Gemini laser system has been operating at a high repetition rate for high intensity (0.5PW) experiments for a number of years and the Central Laser Facility has developed a target methodology to deliver to the user community the maximum number of solid targets and to fully utilise the available time on the laser. Targets for the High Accuracy Microtarget Supply (HAMS) system have been tested and have been proven to survive in a manner to allow shot rates comparable with the available laser repetition rate (0.1Hz). Investigations into target geometry have been carried out and debris production has been studied by high frame rate camera imaging. The study of the relationship between target geometry and debris production has allowed the design of optimal target support infrastructure, such as aperture size and structure, for high rep rate experiments on the Gemini system.

Giant electromagnetic pulses (EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers (e.g. the Extreme Light Infrastructure). We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP, providing an opportunity for comparison with existing charge separation models.

The Target Fabrication group at the Central Laser Facility (CLF) works to develop and produce novel targets for the high-power laser community. Targets range from simple foils to more complex geometries and with many components and key part of the research is materials development. We describe the recent advances in the CLF in surface preparation for electroplating and the manufacture of thin films. Characterisation of these materials is carried out using Atomic Force Microscope and Scanning Electron Microscopy. These advances have been applied to target components that have been used experimentally on the Vulcan Laser system at the Rutherford Appleton Laboratory.

Many of the new large European facilities that are in the process of coming online will be operating at high power and high repetition rates. The ability to operate at high repetition rates is important for studies including secondary source generation and inertial confinement fusion research. In these interaction conditions, with solid targets, debris mitigation for the protection of beamline and diagnostic equipment becomes of the upmost importance. These facilities have the potential to take hundreds, if not thousands, of shots every day, creating massive volumes of debris and shot materials. In recent testing of the Central Laser Facility's High Accuracy Microtargetry Supply (HAMS) system on the mid-repetition rate Gemini facility (15 J, 40 fs, 1 shot every 20 seconds), diagnostics were deployed in order to specifically look at the debris emitted from targets designed for high repetition rate experiments. By using a high frame rate camera, it has been possible to observe and characterize some of the debris production, whilst also looking at target fratricide. Alongside these results from Gemini, we also present results of static debris measurements undertaken on the Vulcan Petawatt high energy, high power facility, where the cumulative effects of debris produced by high power laser experiments have been observed.

The bremsstrahlung x-rays from a laser-solid interaction have been investigated for the use of radiography. The scaling of the x-rays as a function of energy has been characterized and modelled and agrees with previous measurements.

Point-like sources of X-rays that are pulsed (sub nanosecond), high energy (up to several MeV) and bright are very promising for industrial and security applications where imaging through large and dense objects is required. Highly penetrating X-rays can be produced by electrons that have been accelerated by a high intensity laser pulse incident onto a thin solid target. We have used a pulse length of ~10ps to accelerate electrons to create a bright x-ray source. The bremsstrahlung temperature was measured for a laser intensity from 8.5-12×1018 W/cm2. These x-rays have sequentially been used to image high density materials using image plate and a pixelated scintillator system.

Manufacturing low density targets in the numbers needed for high rep rate experiments is highly challenging. This report summarises advances from manual production to semiautomated and the improvements that follow both in terms of production time and target uniformity. The production process is described and shown to be improved by the integration of an xyz robot with dispensing capabilities. Results are obtained from manual and semiautomated production runs and compared. The variance in the foam thickness is reduced significantly which should decrease experimental variation due to target parameters and could allow for whole batches to be characterised by the measurement of a few samples. The work applies to both foil backed and free standing foam targets.

The search for target materials suitable for High Power Laser Experiments at ultralow thicknesses (below ten nanometres) is ongoing. Diamond-Like Carbon is investigated as an answer for a low-Z material that can survive target chamber pump-down and laser prepulse. DLC was produced using Plasma-Enhanced Chemical Vapour Deposition, using with varying gas flow mixtures of argon and methane. The methane plasma deposits amorphous carbon onto the substrate and the argon plasma re-sputters the weakly bonded carbon leaving a high proportion of diamond-like bonding. Bonding natures were probed using Raman spectroscopy; analysis of the resulting spectrum showed that flow rates of 40sccm/60sccm methane to argon produced DLC films with a diamond-like (sp3) content of ∼20%. Increasing the methane gas flow decreased this value to less than 5%. DLC foils were processed into laser targets by method of float off; using a sodium chloride release layer and lowering into water, this was then lifted onto an array of apertures allowing for laser irradiation of the material with no backing. DLC with 20% sp3 content showed superior yield when compared to other materials such as metals and some plastics of the same thickness, with ∼70% of the target positions surviving the float off procedure at <10nm. As a result of this work DLC targets have been available for a number of experiments at the Central Laser Facility.

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.

The Target Fabrication group is responsible for the delivery of high specification microscale targets for irradiation in high power laser experiments. Targets vary in composition depending on the experimental aims and their production and delivery requires extensive expertise in thin-film coating, and characterization as well as a range of other techniques. Thin foil targets are amongst the most widely used target types but the chemical and structural information of such targets on the nanometer scale is not well understood. Collaboration between Target Fabrication (TF), Ultra and Octopus has enabled the development of the capacity to carry out Tip Enhanced Raman Spectroscopy (TERS). On the cutting edge of scanning probe microscopy science, TERS provides the powerful chemical and structural characterization of Raman spectroscopy combined with the high spatial resolution achieved through Atomic Force Microscopy (AFM). The prime aim for the technique is to gain a better understanding of Diamond-Like Carbon (DLC) which has been used successfully as a target material down to a few nanometers in thickness; a regime for targets that is completely unachievable with most materials. A better understanding of the chemical and structural nature of DLC has the potential to lead to even thinner foils.

Pulsed beams of energetic x-rays and neutrons from intense laser interactions with solid foils are promising for applications where bright, small emission area sources, capable of multi-modal delivery are ideal. Possible end users of laser-driven multi-modal sources are those requiring advanced non-destructive inspection techniques in industry sectors of high value commerce such as aerospace, nuclear and advanced manufacturing. We report on experimental work that demonstrates multi-modal operation of high power laser-solid interactions for neutron and x-ray beam generation. Measurements and Monte Carlo radiation transport simulations show that neutron yield is increased by a factor similar to 2 when a 1 mm copper foil is placed behind a 2 mm lithium foil, compared to using a 2 cm block of lithium only. We explore x-ray generation with a 10 picosecond drive pulse in order to tailor the spectral content for radiography with medium density alloy metals. The impact of using >1 ps pulse duration on laser-accelerated electron beam generation and transport is discussed alongside the optimisation of subsequent bremsstrahlung emission in thin, high atomic number target foils. X-ray spectra are deconvolved from spectrometer measurements and simulation data generated using the GEANT4 Monte Carlo code. We also demonstrate the unique capability of laser-driven x-rays in being able to deliver single pulse high spatial resolution projection imaging of thick metallic objects. Active detector radiographic imaging of industrially relevant sample objects with a 10 ps drive pulse is presented for the first time, demonstrating that features of 200 mu m size are resolved when projected at high magnification.

A portable differential image motion sensor (DIMS) has been developed and field demonstrated to measure the atmospheric coherence diameter, or Fried parameter, r(0), both at daytime and at night. The hardware design was developed using system requirements and performance analysis. A graphical user interface (GUI) and software were developed to automatically measure r(0) from collected imagery data. The DIMS system uses a short wave infrared (SWIR) camera, IR telescope with custom environmental enclosure, a rack-mount computer accessed remotely through a laptop, and an equatorial mount and tripod for accurate pointing at a selected star. The system is two-man portable. The sensor continuously measures r(0) from star imagery during clear weather at any time of day or night, with an update rate of 10 minutes. A continuously nutating optical wedge moves the star image in a circle allowing automatic background subtraction. Data output is provided at the SWIR 1.6 mu m wavelength and scaled to 0.55 mu m and pointing at zenith. Valid r(0) measurements range is from 1 cm to 20 cm (in the visible waveband). The r(0) measurements over time were performed at daytime at sea level in San Diego. The largest values of r(0) were observed near and after the sunset. This approach provides a straight-forward path to sea-based seeing measurements with an addition of a stabilized platform.

This paper describes an 0.75 meter aperture, Stabilized High-accuracy Optical Tracking System (SHOTS), two of which are being developed by Textron Systems Corporation, under contract to the Navy's Space and Naval Warfare Systems Center, San Diego (SPAWAR-SD). The SHOTS design is optimized to meet the requirements of the Navy's Theater Ballistic Missile Defense (TBMD) testing program being conducted at the Kauai Pacific Missile Range Facility (PMRF). The SHOTS utilizes a high-precision, GPS aided inertial navigation unit (INU) coupled with a 3-axis, rate gyro stabilized mount which allows precision pointing to be achieved on either land or sea-based platforms. The SHOTS mount control system architecture, acquisition, tracking and pointing (ATP) functionality and methodology which allows the system to meet the TBMD mission data collection requirements are discussed. High frame rate visible and MWIR sensors are incorporated into the system design to provide the capability of capturing short duration events, e.g., missile-target intercepts. These sensors along with the supporting high speed data acquisition, recording and control subsystems are described. Simulations of the SHOTS imaging performance in TBMD measurement scenarios are presented along with an example of the image improvement being achieved with post-processing image reconstruction algorithms.