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The performances degraded by local defects are decomposed into three fields: (i) laser induced damage of these defects, (ii) scattered power, (iii) fratricide effect. The quality of these components cannot be perfect: there are some imperfections on their surface which can reduce the performances of the laser facilities. The high power lasers dedicated to inertial confinement fusion such as the Laser MégaJoule (LMJ) in France, the National Ignition Fusion (NIF) in the USA or the SG-III in China involve thousands of large optical components. We show good agreement between observed diffraction patterns downstream of real defects and model predictions, in terms of “hot spots” generation. These results allowed to specify defects dimensions and nature. In any case, upper bounds of intensifications can be provided as well as safe areas where intensification has decreased enough.
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The accuracy of these predictions will depend on the degree of knowledge of the model parameters set. Defects are modeled by concentric quasi-circular rings of different radii, transmissions and phase shifts. We show in this paper that a simple analytic model can predict light intensification (responsible for some fratricide laser damage) with a high reliability. Borderline cases are then generally processed through timeconsuming optical profilometer measurements that are used in complex numerical laser propagation. So, determining general rules seem to be an impossible task. Indeed, one often has only partial information on each of the (often numerous) defects whereas the light behavior downstream strongly depends on the defect nature and morphology. Indeed, the wave degradation and the ensuing laser performances losses with regard to focal spot or downstream laser induced damage seem hard to predict. Specification of visual defects (scratch and digs) on optics used in high-power laser facilities has always been a headache.