Abstract

We have designed, fabricated and tested 80-cm aperture phase plates for smoothing the Nova laser beams in the target plane. The phase plate consists of a spatially random two-dimensional pattern of bilevel hexagonal elements which introduce a relative phase delay of 0 or π. Fabrication of phase plates involves deposition of a SiO₂ pattern on a SiO₂ substrate through a sequence of chemical and optical steps. We have measured and analyzed the near field diffraction pattern produced by such phase plates and chosen to place them behind the target focus lens to minimize the threat of optical damage. The phase plate properties are characterized by measuring the far-field and the quasi far-field diffraction pattern in terms of the spatial Fourier distribution of intensities. We will discuss theoretical modeling of the performance of these phase plates including a description of the phase aberrations of the Nova beam. We will compare the predicted performance of the phase plates with the measured characteristics.

© 1990 Optical Society of America