Accurate laser damage testing for Laser MégaJoule (LMJ) fused silica optics is crucial for predicting their lifetimes. However, beam propagation in optics is usually neglected and yet, damage sites are mostly initiated on the exit face of optics. The MELBA testbed in CEA CESTA (France) delivers nanosecond UV laser pulses representative of LMJ optics conditions on a centimeter scale. Our particular imaging system measures the beam spatial profile before and after propagation in samples, enabling quantification of self-focusing induced by the Kerr effect. This metrology is necessary for laser damage parametric studies, particularly when these laser parameters influence the Kerr effect. We present here a study of the impact of a linear-to-circular polarization conversion on laser damage, which highlights the importance of accurately assessing non-linear beam propagation for laser damage tests.
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