Laser decoy is widely used in the field of electro-optical countermeasures, against laser guided semi-automatic weapons. Decoy laser usually includes a laser light source with specific wavelength and signal, whose energy distribution has Lambertian reflection characteristics. With a 633nm laser source, a fibre and a diffusive module, a homogeneous field laser was illustrated, which was generated through high-density colloidal dispersion to get diffused. By optimizing the fibre and structure parameters, the laser light energy utilization was improved while maintain light field uniformity. Additionally, the flat field system was designed and tested using high reflectivity PTFE material, with a reflectivity of 97%. A developed Lambertian light source system for reference-based Laser decoy was established, whose non-uniformity was lower than 0.3%. The results showed that the Lambertian light source system could meet the requirement of Laser decoy, and needed to be improved in near infrared.
The effects of laser irradiation on materials include thermal ablation, shock and radiation, where the thermal ablation is the major one in industrial application. When the laser beam irradiates the target, the temperature rises rapidly from the outside in until reaching a certain temperature. The material is melted even gasification. The steam expands and splashes, while washing away the molten material in liquid or solid state and forming pits or perforation. The effect of thermal ablation is related to the parameters of laser source, the external environment parameters and the material parameters. The parameters of the laser source include the wavelength, power density, irradiation time, CW or pulse and the pulse length. The short pulse laser mainly ablated the material by reaching the threshold of power density, while the long pulse laser by reaching the threshold of energy density. In this paper, a dual pulse length method is discussed and theoretically analyzed. A dual pulse length laser with nanosecond and microsecond pulse length is used. The experiment is carried on in three situations: only microsecond laser, only nanosecond laser and both. Experiment results show that the short pulse laser is much better than the long pulse laser under the same average power condition. When the dual pulse width laser is irradiated and the exposure time is accurately matched, the effect is greatly improved and the damage threshold is decreased by one order of magnitude.
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