We have performed experiments using Callisto, the Vulcan 100 TW and the Vulcan Petawatt high intensity lasers to understand the characteristics of high energy, Kα x-ray sources and to implement workable radiography solutions at 20-100 keV. Our measurements show that the Kα size from a simple foil target is larger than 60 µm, far larger than the experiment resolution requirement. The total Kα yield is independent of target thicknesses verifying that refluxing plays a major role in photon generation. Smaller radiating volumes emit brighter Kα radiation. 1-D radiography experiments using small-edge-on foils resolved 10 µm features with high contrast.We tested a variety of small volume 2-D point sources such as cones, wires, and embedded wires, measuring photon yields and comparing our measurements with predictions from hybrid-PIC LSP simulations. In addition to high-energy, high-resolution backlighters, future experiments will also need imaging detectors and diagnostic tools that are workable in the 20-100 keV energy range. An initial look at some of these detector issues is also presented.

Time-resolved x-ray spectra from solid targets irradiated by the VULCAN Petawatt laser focused to 1020Wcm−2 show that material at solid density is heated to temperatures above 500 eV to a depth of about 15 μm and for a duration of more than 30 ps. Modeling with the implicit hybrid plasma code LSP shows that the heating is sensitive to the laser prepulse through resistive inhibition of the laser accelerated electrons in the blow off layer.

IntroductionSince the construction of the first Petawatt laser on the Nova laser facility at Lawrence Livermore National Laboratory we are witnessing the emergence of similar Petawatt-class laser systems at laboratories all around the world [i]. This new generation of lasers, able to deliver several hundred joules of energy in a sub-picosecond pulse, has enabled a host of new discoveries to be made and continues to provide a valuable tool to explore new regimes in relativistic laser-plasma physics-encompassing high energy X-rays and -rays, relativistic electrons, intense ion beams, and superstrong magnetic fields [ii,iii,iv]. The coupling in the near-future of multi-kiloJoule Petawatt-class lasers with large-scale fusion lasers-including the NIF and Omega EP (US), LIL (France), and FIREX (Japan)-will further expand opportunities in fast ignition, high energy X-ray radiography, and high energy density physics research.

A free-standing gold transmission grating with a period of 5000 Å has been coupled to a soft x-ray sensitive streak camera with a limiting temporal resolution of 10 ps. The streak camera is equipped with a caesium iodide transmission photocathode and observations have been made in the 10-100 Å regime. For a small source (200 m diameter) the spectral resolution is predicted to be around 2.5 Å. This has been confirmed by examination of the Lyman-␣ line in hydrogen-like laser heated boron. A recorded linewidth of 2.44 Å is demonstrated. The instrument has been used to diagnose the soft x-ray emission from a plastic (CH) foil target heated by an ultra-intense ͑2 ϫ 10 20 W cm −2 ͒ laser pulse.

Electron–optic streak chronoscopy is an important diagnostic technique for the diagnosis of laser driven hydrodynamic and radiative phenomenon. To minimize the undesirable effects of excessive space charge in streak image tubes an image amplification stage is often used. Microchannel plate (MCP) electron amplifiers are frequently employed for this purpose. These devices may be utilized in two ways: either to amplify light from the streak image tube phosphor screen by externally coupling a proximity-focus MCP wafer intensifier tube, or by insertion inside the streak tube body to amplify the streaked electrons directly. To investigate how the operating regime of the MCP influences the dynamic range of the streak camera system, dynamic range measurements have been made on two identical streak image tubes (English Electric Valve Co. type P8307) one incorporating an internal MCP, the other, externally coupled image amplification. Dynamic range measurements have been made for 30 ps full width half maximum (FWHM) and 100 ps (FWHM) laser pulses and comparison made to a previous study of this type of image tube. For internal MCP and externally coupled intensifier camera systems of equal radiant gain the dynamic range for the pulse widths studied was found to be comparable.