论文部分内容阅读
在过去的十年,用激光产生和接收超声的技术引起了很大的兴趣。 当高功率的激光脉冲入射在金属表面上,部份电磁能量被吸收并转换为热能,吸收发生在“趋肤深度”之内,典型的深度是几个毫微米。这时会出现两种情况,一种是热弹效应,温度可能上升几十度或几百度,从而在很薄的金属表层中产生了瞬时的热弹应力和应变。另一种情况是,当激光束功率密度大于100MWcm~(-2),金属表面将被烧蚀。两种情况下都可产生纵波、横波和表面波。
In the past decade, the use of laser to generate and receive ultrasound technology has aroused great interest. When a high-power laser pulse is incident on a metal surface, part of the electromagnetic energy is absorbed and converted to heat, which takes place within the “skin depth,” a typical depth of a few nanometers. There are two situations at this moment, one is the thermoelastic effect, the temperature may rise tens or hundreds of degrees, resulting in a thin metal surface instantaneous thermo-elastic stress and strain. Alternatively, the metal surface will be ablated when the laser beam power density is greater than 100 MWcm -2. In both cases can produce longitudinal waves, shear waves and surface waves.