Wavefront and Divergence of the Beamlet Prototype Laser

We have measured the wavefront and the divergence of the Beamlet prototype laser under a variety of conditions. Emphasis of the tests was on quantifying best attainable divergence in the angular regime below 30 prad to benchmark propagation models that are used to set wavefront gradient specifications for NIF optical components. Performance with and without active wavefront correction was monitored with radial shearing interferometers that measured near-field wavefront at the input and output of the main amplifier with a spatial resolution of 1 cm, and cameras which measured the corresponding intensity distributions in the far field with an angular resolution of 0.3 prad. Details of the measurements are discussed and related to NIF focal spot requirements and optics specifications.