The propagation of a high-energy laser (HEL) beam through the atmosphere causes stray light emission of much higher average intensity than from conventional cw or pulsed laser sources. Particularly interesting are the events of laser emission interaction with aerosol and dust particles, leading to powerful scattered radiation pulses. Their peak power may significantly exceed the average level of the scattered emission and may seriously impact evaluation of nominal ocular hazard distance (NOHD) and thus laser safety aspects of HEL outdoor operations.
The laser radar cross section (LRCS) is a parameter for describing the reflective properties of targets, illuminated by laser light. As the role of lasers in remote sensing continues to grow in the automotive, or military fields, a proper measurement methodology for the laser radar cross section of various objects, especially in a laboratory environment, is crucial. In this contribution we performed preliminary investigations in a laboratory environment on the laser cross section of different optical components such as mirrors. The research focus hereby is put on the influence of various measurement parameters of the setup with respect to the measured LRCS. Such parameters are for example different angles of incidence, beam size and beam quality.
Fraunhofer IOSB (Ettlingen, Germany) developed and built a measurement system to verify laser threat detection. The system has been given the name MARLA (Maritime Lasermessanlage), eng.: maritime laser measurement system. It is an integral part of an exercise and test range for electronic warfare of the German Navy at Wehrtechnische Dienststelle für Schiffe und Marinewaffen, Maritime Technologie und Forschung WTD 71, Eckernförde, Germany.
The system provides realistic simulations of various laser-based threats to ships on sea and allows studies of the efficacy of onboard laser warning receivers. MARLA assists laser counter-measures and enables to include environmental studies (atmospheric transmission, water reflections etc.). Redundant system design ensures laser safety even in public areas.
The core of MARLA is a modular laser unit (LU) consisting of five laser modules (LM) and the dedicated laser controllers (LC). The laser modules are mounted on a pan-tilt positioner. MARLA covers the most common laser threats like laser target designator (LTD), laser range finder (LRF), laser beam rider (LBR) and laser dazzler (LD). The individual laser modules are based on commercially available laser sources fitted with multi-stage attenuators to set the laser irradiance within a range of seven orders of magnitude without losing beam quality. By means of a photo detector, the energy of the emitted laser pulses is recorded. An integrated beam shaper enables to vary the beam divergence.
The further crucial parts of MARLA are the control and data acquisition system with operating and visualization software and a general laser safety monitoring system. All the subsystems are integrated into a climate-controlled movable 20' sea container. Use of a stand-alone verification system provides reference data to verify the actual on-site irradiation at the test target.
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