Nanosecond multipulse retinal damage thresholds of elongated irradiance profiles in explant measurements and simulations.

Significance: The database for multipulse retinal damage thresholds for the laser safety standard (IEC 60825-1:2014) is confined, especially for elongated irradiation profiles. To ensure eye safety, retinal damage thresholds (ED50 values) need to be determined. Aim: This study aims to examine nanosecond multipulse scenarios. Approach: To determine ED50 values in ex vivo measurements, an optical laser setup is presented. Porcine explant tissue is irradiated with rectangular top-hat profiles. Thermal simulations are carried out on a validated computer model and retinal injury thresholds are obtained. Results: The measurements resulted in ED50 values from 8.46 to 42.72 µJ with a slope from 1.15 to 1.4. A thermal damage in the measurements can be excluded due to the level value in combination with a different type of declining behavior for increasing pulses compared to the simulations. A dependence with increasing elongation or area of the retinal image emerges in the simulations but could not be confirmed in the measurements due to the influencing factors (biological variability, focusing, and measuring procedure). Conclusions: Using slit apertures for beam shaping, variable rectangular spot geometries are realized without changing elements in the setup. For further evaluation of the behavior of elongated irradiation profiles, additional measurements to improve the measurement accuracy are necessary.

Wave optical simulation of retinal images in laser safety evaluations.

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.