Li Zheng, Lomonosov Alexey M, Ni Chenyin, Han Bing, Shen Zhonghua
Opt Lett. 2018 Jan 1;43(1):78-81. doi: 10.1364/OL.43.000078.
This Letter focuses on the selectively non-contact generation of Lamb wave modes in plates by using a continuous-wave (CW) laser moving along sample surface. Compared with the generated Lamb waves with broadband, multiple modes (the existence of at least two modes at any given frequency) excited by a pulsed laser, the desired single narrowband mode of the Lamb wave can be generated by a moving CW laser, as long as the scanning speed matches the phase velocity of the mode. Moreover, the dispersion curves of the Lamb wave can be obtained directly from the power spectrum of the time-domain signal recorded at each laser's moving speed. Single A mode excitation, coupled resonance phenomenon of A mode and S mode, single S mode excitation, and high-order modes appeared successively as scanning speed increased. Especially, the excitation of the pure single S mode can be realized, which is suitable for propagation in the case of liquid loading. It is proposed, for the first time to the best of our knowledge, to realize the selection of a single Lamb wave mode by using the CW laser scanning method, which provides a brand-new way for laser ultrasonic excitation.
本文聚焦于通过沿样品表面移动的连续波（CW）激光在板中选择性地非接触产生兰姆波模式。与脉冲激光激发的具有宽带、多模式（在任何给定频率下至少存在两种模式）的兰姆波相比，只要扫描速度与该模式的相速度匹配，移动的连续波激光就能产生所需的单窄带兰姆波模式。此外，兰姆波的色散曲线可直接从在每个激光移动速度下记录的时域信号的功率谱中获得。随着扫描速度增加，依次出现单A模式激发、A模式与S模式的耦合共振现象、单S模式激发以及高阶模式。特别是，可以实现纯单S模式的激发，这适用于液体负载情况下的传播。据我们所知，首次提出通过连续波激光扫描方法实现单一兰姆波模式的选择，这为激光超声激发提供了一种全新的方式。
