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Spatial filter pinhole development for the national ignition facility.

We present results from a major experimental effort to understand the behavior of spatial filter pinholes and to identify and demonstrate a pinhole that will meet the requirements of the National Ignition Facility (NIF). We find that pinhole performance depends significantly on geometry and material. Cone pinholes are found to stay open longer and to cause less backreflection than pinholes of more conventional geometry. We show that a +/-150-microrad stainless-steel cone pinhole will pass a full-energy NIF ignition pulse with required margins for misalignment and for smoothing by spectral dispersion. On the basis of a model fitted to experimental results, a +/-125-microrad stainless-steel cone pinhole is also projected to meet these requirements.