金属中激光超声的产生及应用

Generation and Application of Laser Ultrasonics in Metals

介绍了用不同脉宽、不同波长的钇铝石榴石(Nd:YAG)激光在不同厚度的金属样品中产生超声脉冲的实验。超声波的接收是用聚偏氟乙烯薄膜(PVDF)实现的。文中给出了激光超声脉冲及其在金属板中的回波的波形曲线;测量了不同条件下激光超声幅度与激光能量的关系,超声幅度与激光波长的关系,以及超声脉宽和激光脉宽的关系;观察到了激光超声的传播方向总是沿被照表面的法线方向,而与激光的入射角无关。实验结果表明,激光超声作为一种非接触的超声源,对于工业应用尤其是高温运动状态下对弯曲表面的工件(如管材等)进行厚度测量和探伤具有广阔的应用前景,也将是激光与物质相互作用领域的一种重要研究手段。

Ultrasonic pulses have been generated in metal samples of various thickness by irradiation of Nd : YAG laser pulse in different pulse width and wavelength. Detection of ultrasound is realized by polyvinylidene fluoride (PVDF) piezoe- lectric film. The wave charts of laser ultrasonic pulse and its echoes in metal plate are shown. The relationships between 1) ultrasonic amplitude and laser energy, 2) ultrasonic amplitude and laser wavelength, and 3) ultrasonic pulse width and laser pulse width are given out. It is observed that the propagation direction of laser ultrasound is independent to that of laser and always perpe- ndicular to the irradiated surface. It is pointed out that, as a non-contact ultra- sonic source, laser ultrasonics is very advantageous to industrial application, especially for on-line thickness measurement of hot, moving workpieces with curved surface such as hot-rolled steel tubes. It will also play an important role in research fields of interaction between laser and matter.