This paper describes the characteristics of the vibration of an electric insulator irradiated impulsively by a TEA-CO2 laser beam, and the possibility of the distinction of the cracked sample by detecting the vibration remotely with a He-Ne laser interfeometer. The amplitude of the vibration, monitored by the acceleration sensor touched on the smaple, depends on the laser output energy and the distance between the surface of the sample and the Germanium lens to focus the laser beam on the sample. These characteristics can be explained by the thermal shock by the heating of laser beam, the reaction of the particles spouting from the sample and the shock wave from the air breakdown induced by laser beam in front of the sample, and it is confirmed that the reaction of the spouting particles mainly causes the sample to be vibrated. It is suggested that the cracked sample can be distinguished by estimating the difference of the frequency spectrum or the damping factor of the vibration between the normal and cracked samples, or by listening the output of the photomultiplier of the interferometer through a speaker under the condition that the laser power density is more than 2×107W/cm2 in this experiment. From the above result, it is also suggested that the sample can be vibrated enough to detect the cracked one from the 40m distance by focussing the laser beam which has the TEM00 mode and the energy of 2 J.
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