Abstract：
Laser ultrasonics is a noncontact measurement method that uses a laser-induced elastic wave source in combination with an optical surface displacement-tracking system. This study compared the performances of two optical interferometers with different characteristics when applied to measurement of pulsed thermoelastic waves. The surface displacement-tracking system was designed to measure the center of the microscopic view. A pulsed laser beam irradiated a black ink layer to generate the thermoelastic waves. The out-of-plane displacement on the axially opposite side was then measured using either a Michelson interferometer or a Sagnac interferometer. The objective lens of the system was of a type commonly used in biological observations. The Michelson interferometer estimated a maximum displacement of 0.43 nm and a maximum sound pressure of 24.7 kPa. The signal-to-noise ratios from 16 averages were 14.9 dB (Michelson interferometer) and 19.2 dB (Sagnac interferometer). Furthermore, this paper compares the performance of the numerically estimated Sagnac interferometer outputs calculated from the measured Michelson interferometer outputs with the experimentally obtained Sagnac interferometer outputs. The numerically estimated Sagnac interferometer\'s output was shown to be identical to the experimentally acquired output. The Michelson interferometer requires a higher average operating frequency (i.e., it needs a longer data acquisition time), although this interferometer does offer superior displacement output linearity. This property enables calculation of the sound pressure from the displacement amplitude. These findings indicated that combination of the measurement points of the Sagnac interferometer with those of the sparsely distributed Michelson interferometer reduced the measurement time when compared with a single use of the Michelson interferometer while also maintaining the data acquisition quality.
摘要：
激光超声是一种非接触式测量方法，它使用激光诱导的弹性波源与光学表面位移跟踪系统相结合。这项研究比较了两种具有不同特性的光学干涉仪应用于脉冲热弹性波测量时的性能。设计了表面位移跟踪系统来测量微观视图的中心。脉冲激光束照射黑色油墨层以产生热弹性波。然后使用Michelson干涉仪或Sagnac干涉仪测量轴向相对侧上的平面外位移。该系统的物镜是生物观测中常用的类型。迈克尔逊干涉仪估计的最大位移为0.43nm，最大声压为24.7kPa。16个平均值的信噪比分别为14.9dB（迈克尔逊干涉仪）和19.2dB（萨格纳克干涉仪）。此外，本文比较了从测量的迈克尔逊干涉仪输出计算的数值估计的Sagnac干涉仪输出与实验获得的Sagnac干涉仪输出的性能。数值估计的Sagnac干涉仪的输出与实验获得的输出相同。迈克尔逊干涉仪需要更高的平均工作频率(即，它需要更长的数据采集时间)，虽然这种干涉仪确实提供了优越的位移输出线性度。该特性使得能够根据位移振幅来计算声压。这些发现表明，与单次使用Michelson干涉仪相比，Sagnac干涉仪的测量点与稀疏分布的Michelson干涉仪的测量点的组合减少了测量时间，同时还保持数据采集质量。
