We performed simulations and experiments of wavefront distortions induced by propagating through diode-pumped square-section amplifying laser rods of Nd-doped phosphate glass and 0.5 % N d : 5 % L u : C a F 2 . We observed that depending on the material, wavefront distortions’ profile can vary from a circular lens-like distortion to a complex astigmatic distortion. We showed that this difference comes from the relative sign of piezo-optic tensor coefficients.

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Two centuries ago, Fresnel, Poisson, and Arago showed how the wave nature of light induces a bright spot behind an opaque disk. We develop an analytical model based on the Fresnel diffraction theory to show how small perturbations such as digs or scratches can yield intense light enhancements on the downstream axis. The impact of defects with complex morphology on light diffraction is shown to be accurately modeled by the Fresnel theory applied to a set of opaque disks characterized by phase shift and transmittance. This model can be used either to define the geometry of the defects that optimizes the light enhancement or to improve the defect specification on the surface of the optical components. We explain why partial information of the defect morphology can suffice to specify a safety distance beyond which light intensifications are not dangerous. The validity of this analytical approach is studied by measuring the intensifications created by three different microdefects.

Fused silica optics often exhibit surface scratches after polishing that radically reduce their damage resistance at the wavelength of 351 nm in the nanosecond regime. Consequently, chemical treatments after polishing are often used to increase the damage threshold and ensure a safe operation of these optics in large fusion-scale laser facilities. Here, we investigate the reasons for such an improvement. We study the effect of an HF-based wet etching on scratch morphology and propose a simple analytic model to reflect scratch widening during etching. We also use a finite element model to evaluate the effect of the morphological modification induced by etching on the electric field distribution in the vicinity of the scratch. We evidence that this improvement of the scratch damage resistance is due to a reduction of the electric field enhancement. This conclusion is supported by secondary electron microscopy (SEM) imaging of damage sites initiated on scratches after chemical treatment.