TNO has expanded its 30 kW HEL research facility with the capability to monitor specular and diffuse reflections of the laser beam. A capture screen and high-speed camera focus on dynamic specular reflections, while 15 individually placeable probes monitor the diffuse component under different angles. This paper introduces the reflection measurement capability and discusses the behaviour of steel and aluminium coupons under high-energy laser irradiation. Laser-material interaction was found to be rather predictable in thermal behaviour up to the perforation event. Reflections, however, showed a highly dynamic pattern, varying in magnitude and direction and depending on bulk material, material surface condition, phase state of the material (solid or liquid) and geometry. The difficulty of assessing proper stand-off distances for laser safety is illustrated.
Fielding TNO's LPT (Laser Propagation Testbed) for the first time in an international trial, a 3.6 km optical propagation path was created in a maritime environment between the city of Den Helder and the island of Texel in the Netherlands. Using a 1 W, 1556 nm laser beam, atmospheric propagation was investigated by capturing the resulting beam profile on a capture plate, which was imaged with a high-speed SWIR camera. Meteorological conditions were monitored using standard meteo stations, two visibility meters, two scintillometers and aerosol equipment. Over two weeks of measurements, propagation conditions varied from windy with clear, blue skies to significantly limited visibility. In this paper, the setup is introduced and a first discussion of the relation between beam behaviour and meteorological conditions is presented.
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