Whereas laser weapon systems are foreseen as a new possibility to counter unmanned aerial vehicles (UAVs), a better understanding of the complex phenomena occurring during the interaction of a high-energy laser beam with a flying structure is required to use those new innovative defense devices in an efficient but also a secure way. This paper first presents multiple material characterizations performed on glass fibers-reinforced plastics (GFRP), from which near-infrared spectroscopic data and high-temperature thermodynamic results are later implemented into multiphysics simulations. Numerical outcomes from the models are then compared to experimental recordings arising from laser trials carried out with varying power densities (75, 150 and 300 W/cm2) and with illumination times of several seconds. A very good agreement is shown between temperature data collected during laser experiments and temperature values from computations.
The attenuation or "limitation" of an incoming laser threat to a safe level of radiations using an external element is called optical limitation. The concept of passive laser protection requires the use of materials with nonlinear optical properties that are self-activated when the incident laser threat is above a certain level of intensity. Conjugated polymers are tailored for optical limitation due to their versatility, their non-negligible nonlinear absorption properties and their uniform transmittance characteristics over a broad spectral range, the latter property avoiding color distortions to the observer. Usually, to obtain an optical limiting filter, nanomaterials are dispersed in a polymer host. In this work, we consider polyvinylcarbazole (PVK) as a new polymer host for optical limiting filters. PVK is a high Tg polymer exhibiting a high linear transmittance over a broad spectral range, up to 1.6 μm. The adiabatic bulk polymerization method has been employed to thermally polymerize the monomer in the presence of an initiator. Traces of remaining monomer have qualitatively been monitored using FTIR spectroscopy. Optical limiting experiments have been conducted at the wavelength of 1.06 μm using a Nd:YAG laser source in the nanosecond pulsed regime at a low pulse repetition rate. PVK-based filters present a low nonlinear threshold (i.e. activation of the nonlinear attenuation), a factor of 10 lower than the usual PMMA-based filters. Their global nonlinear attenuation is as high as OD = 2.0.
In this work the potential of THz technology to detect ageing effects in modern armor system is studied. First experiments have been done in pure polymers, a key component in modern armor devices. Artificial ageing in thermooxidative environment has been applied to Polyamide 6 and Polyethylene and their THz response has been recorded. It was found that the THz refractive index indeed undergoes significant changes after the thermal treatment. The direction of the changes and the mechanisms causing these changes are highly dependent on the investigated polymer. Afterwards experiments on more representative devices, made from hard aramid, were conducted. An artificial ageing following the NATO standard STANAG 4370 has been applied. The THz refractive index undergoes significant changes, showing the high potential THz technology has to offer in this novel field of application.
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