Measurements of the effects of the intensity pickets on laser imprinting for direct-drive, adiabat-shaping designs on OMEGA

Effects of the intensity pickets on laser imprinting were investigated using laser-driven, planar plastic and foam targets on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Intensity pickets are used in adiabat-shaping techniques designed to improve stability of inertial confinement fusion targets. The measurements were performed in planar foam targets using the decaying shock method of adiabat shaping and in planar plastic targets using the relaxation (RX) method. In foam targets, the picket reduced the target areal-density modulations by ∼6 times at shorter spatial wavelengths of 30 and 60μm, while at a longer wavelength of 120μm there was no reduction. The “imprint efficiency,” the equivalent surface amplitude produced by imprinting, was reduced by the intensity picket by a factor of ∼3 at a spatial wavelength of 60μm, while it was increased by a factor of ∼2 at a 120-μm spatial wavelength. In plastic targets, used to test the RX method, the imprint efficiency was reduced by the intensity picket by a factor of ∼2 at spatial wavelengths of 30 and 60μm, while it was about the same at a 120-μm spatial wavelength.