Abstract
When a continuously oscillating CO2 laser beam is irradiated to the surface of water, an impact sound is produced; in addition, a crater is formed on the water surface. The process by which an impact sound is produced, and a crater is formed, when a CO2 laser beam of 7.5-21 W is irradiated to the surface of water was investigated using a high-speed video camera (2000 frames/second) and a high-sensitivity condenser microphone having a reaction time of 0.5 × 10-6 second in the 10-35 kHz frequency range. As a result, the following was determined. (1) The source of the impact sound is created on the water surface. (2) An impact sound is produced from the water surface, and a crater is formed on the water surface, when the power density of the laser beam irradiated to the water surface is in the range, 8 × 106 - 4 × 107 W/m2. (3) As time passes, the crater grows to a hemispherical shape with a diameter of 2 × 10-3 m, and then collapses and disappears. The time required for this is approximately 5 × 10-3 second.
