Modeling of Laser Knife-Edge and Pinhole Experiments

We describe simulations of experiments involving laser illumination of a metallic knife edge in the Optical Sciences Laboratory (OSL) at LLNL, and pinhole closure in the Beamlet experiment at LLNL, The plasma evolution is modeled via LASNEX. In OSL, the calculated phases of a probe beam are found to exhibit the same behavior as in experiment but to be consistently larger. The motion of a given phase contour tends to decelerate at high intensities. At fixed intensity, the speed decreases with atomic mass. We then calculate the plasmas associated with 4-leaf pinholes on the Beamlet transport spatial filter. We employ a new propagation code to follow a realistic input beam through the entire spatial filter, including the plasmas. The detailed behavior of the output wavefronts is obtained. We show how closure depends on the orientation and material of the pinhole blades. As observed in experiment, a diamond orientation is preferable to a square orientation, and tantalum performs better than stainless steel.