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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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