Remarkable density structures are observed in the plasma generated during the rise of a high-power COg laser. Jetlike structures and density bowls are seen in interferograms. Infrared imaging shows that these bowls are linked to localized Brillouin-instability backscatter. Depolarization measurements also exhibit filamentary structures that extend far into the underdense regions of the plasma.

Convective Brillouin amplification in inhomogeneous, drifting plasmas is discussed. The bandwidth of the amplifier is a function of both wave damping and plasma inhomogeneity. For any given plasma model and source spectrum, the final amplified spectrum can be constructed, including the effects of inhomogeneity, drift, damping, and gain narrowing. Conversely, the shape of observed spectra of Brillouin scattering can be used to obtain information about conditions in the underdense plasma corona if it can be assumed that amplification is high enough that the final spectral bandwidth is amplifier dominated.

Absolute instability of stimulated Brillouin scattering in drifting plasmas Phys. Fluids 25, 179 (1982); 10.1063/1.863616 Convective amplification of drift waves and thermal fluctuation levels in a stable plasma Phys. Fluids 23, 985 (1980);

CH2, Al, and Pb targets have been irradiated at a maximum flux of 3×1013 W cm−2 with a focused CO2 laser in order to study the effects of nonlinear processes on x-ray emission. A multichannel x-ray spectrometer measured the x-ray spectrum from 1 to 50 keV. Above a critical flux of 6×1012 W cm−2, the results show a change in the slope of soft x-ray intensity versus laser flux, a change in the power-law dependence of hot temperature versus flux, an anisotropy of soft x-ray emission, and a strong production of energetic electrons. With increasing Z, there is no reduction of the effects of nonlinear phenomena, which appeared stronger with Al. The comparison with experiments performed at 1.06 μm suggests that the fraction of laser energy present in fast electrons scales as φλ2.

Overvoltage protection circuits have been developed to protect oscilloscope inputs or other 50-Ω recording systems from fast (τr∼1 ns) rise-time pulses. These circuits are voltage dividers with linear output up to a specified level, typically 1.4 V, beyond which fast switching diodes limit the output to ≲5 V for inputs as high as 5 kV. The clipping circuits are frequency compensated for flat response to several hundred megahertz.