The data situation of laser-induced damage measurements after multiple-pulse irradiation in the ns-time regime is limited. Since the laser safety standard is based on damage experiments, it is crucial to determine damage thresholds. For a better understanding of the underlying damage mechanism after repetitive irradiation, we generate damage thresholds for pulse sequences up to N = 20 000 with 1.8 ns-pulses using a square-core fiber and a pulsed Nd:YAG laser. Porcine retinal pigment epithelial layers were used as tissue samples, irradiated with six pulse sequences and evaluated for damage by fluorescence microscopy. The damage thresholds decreased from 31.16 µJ for N = 1 to 11.56 µJ for N = 20 000. The reduction indicates photo-chemical damage mechanisms after reaching a critical energy dose.

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Lasers with wavelengths in the visible and near infrared region, pose a potential hazard to vision as the radiation can be focused on the retina. The laser safety standard IEC 60825–1:2014 provides limits and evaluation methods to perform a classification for such systems. An important parameter is the retinal spot size which is described by the angular subtense of the apparent source. In laser safety evaluations, the radiation is often described as a Gaussian beam and the image on the retina is calculated using the wave optical propagation through a thin lens. For coherent radiation, this method can be insufficient as the diffraction effects of the pupil aperture influence the retinal image. In this publication, we analyze these effects and propose a general analytical calculation method for the angular subtense. The proposed formula is validated for collimated and divergent Gaussian beams.

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