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We report on experiments using the 100 TW laser at LLNL (40J, 400 fs, 5×1019 W/cm2 focal intensity) and planar multilayer targets (Mo/Sn) to study the generation and transport of electrons with MeV energies. Such fast electrons are of prime importance to many proposed applications, e.g., the fast ignitor fusion concept. X-ray emission spectroscopy is used to study the electron transport. Characteristic K α photon emission produced by the fast electrons in the front (Mo) and rear (Sn) layers of the target is measured with a charge-coupled device detector (single photon counting mode) to infer the electron energy deposition. The electron energy spectrum is measured by varying the thickness of the Mo layer to attenuate the electrons by different amounts. Penumbral imaging of the K α emission is used to give information about the angular distribution of the fast electron emission. Details of the measurement techniques and experimental results will be discussed and compared with modeling calculations.

Experiments were performed using the Lawrence Livermore National Laboratory Nova laser to measure the nonlinear refractive index of air and argon gases via the technique of intensity-dependent ellipse rotation. These measurements directly impact our understanding of beam propagation issues and solid-state frequency conversion performance for large laser systems. Our experimental values for the nonlinear refractive index at 293 K, 1 atm, are ~0.98 × 10−16 esu for air and 0.23 × 10−16 esu for argon. We surveyed the recent literature to compile what we consider the most reliable values for the nonlinear indices of air (nitrogen and oxygen) and argon. This has been accomplished by deducing the third-order susceptibility tensor components for the optical Kerr effect from precise measurements of the dc Kerr effect and electric field-induced second harmonic generation reported in the literature.1 Our ellipse rotation measurements and calculations confirm that the nonlinear indices for air are substantially lower than previously reported.2 Thus nonlinear refraction over long air paths has less impact on diffraction and frequency conversion in large laser systems than previously believed.