Predicting laser damage from interference intensification by input surface mitigation cones

Cones are machined into the surfaces of final fused silica NIF optics to remove laser induced damage. Applied to the input surface they are also to prevent the growth of exit surface damage by generating a shadow over the damage. As a result, cones with different sizes, depths, and shapes are being deployed in greater numbers. The expanding waves from input surface cones produce an intensification pattern at the exit surface from interference between the expanding annular wave from the cone walls and the incident beam. The probability of damage from this intensification will increase if two or more expanding waves overlap. The likelihood of overlap will increase with increasing use of these cones. It is impractical to survey all possible overlap situations through costly damage tests. We will explore alternative diagnostic and analytical tools to predict the probability of damage from the expanding waves of input cones with different degrees of overlap and at the higher NIF energies anticipated in the future.