Pulsed scattering events during HEL atmospheric propagation

When employing a High Energy Laser (HEL) in an outdoor environment, a laser safety evaluation has to consider the energy scattered by aerosols during the propagation of the laser. We developed a measurement device SeLMA (ScattEred Laser Measurement Assembly), comprising a set of optical receivers installed on an arc to perform an angularly- and temporally-resolved measurement of this scattered radiation. Measurements with high laser emission intensities revealed powerful pulses in the scattered radiation with the peak power significantly exceeding the average level of the signal. Radiative intensity distribution of the scattered emission was measured in a controlled laboratory environment at various irradiance levels in the laser beam. These results were used for preliminary evaluations of the off-axis ocular hazard distance for a typical HEL operation scenario.