金屬塊材表面之奈米級動態位移量測，在雷射激發超音波與非破壞檢測中扮演關鍵角色。雷射干涉儀輸出同相（P）與正交（Q）兩道訊號，架構簡單且具奈米級解析度，實際P/Q訊號存在直流偏移、振幅不平衡與正交誤差，使P-Q軌跡由標準圓退化為偏移斜置之橢圓，且待測波動訊號僅有奈米級振幅，遠小於繞行一圈所需之半個波長，校正參數無法由待測訊號本身取得。
本研究以AVID系統架構為基礎重建圓偏振雷射干涉儀，並建立兩階段量測流程，量測前先以壓電致動器（PI P-840.10）走過遠大於半個波長之行程，使P-Q平面繞出完整而圓整之軌跡，以圓擬合求得圓心、半徑與正交性等校正參數，隨後以該圓為基準，逐點計算待測物P/Q訊號之角度變化，經換算重建位移時間歷程。壓電致動器僅為描圓之參考源，校正僅依賴閉合軌跡之幾何，不受其非線性與遲滯影響。
驗證實驗以Nd:YAG脈衝雷射（Continuum Surelite，波長532奈米）照射不鏽鋼（SUS304）試塊，藉熱彈性效應激發表面波，並於激發同一面拾取暫態表面波位移訊號，重建其位移時間圖。
結果顯示，重建後之系統具備量測與分析雷射激發暫態表面波之能力，所建立之「壓電參考圓臨場校正、兩階段位移重建」流程亦可直接沿用於後續量測，為表面波波速量測、材料特性評估與缺陷檢測等延伸應用奠定基礎。

Nanoscale dynamic displacement measurement on bulk metal surfaces is critical to laser-generated ultrasound and non-destructive testing. A laser interferometer outputs in-phase (P) and quadrature (Q) signals, giving nanometer-level resolution with a simple architecture. In practice, DC offsets, amplitude imbalance, and quadrature error degenerate the P–Q trajectory from an ideal circle into an offset, tilted ellipse. Because the signal under test is far smaller than the half-wavelength travel needed for one full circuit, calibration parameters cannot be extracted from the signal itself.
A circularly polarized laser interferometer was therefore rebuilt on the AVID architecture with a two-stage measurement procedure. Before each measurement, a piezoelectric actuator (PI P-840.10) is driven far beyond half a wavelength so that the P–Q plane traces a complete closed trajectory; circle fitting then yields the center, radius, and orthogonality. Using this circle as the reference, the angular variation of the P/Q signals is computed point by point and the displacement history reconstructed through the λ/4π factor. Because calibration depends solely on the geometry of the closed trajectory, the actuator's nonlinearity and hysteresis do not affect the result.
For validation, an Nd:YAG pulsed laser (Continuum Surelite, 532 nm) irradiated a stainless steel (SUS304) specimen to excite surface waves thermoelastically, with the transient displacement detected on the same face as the excitation. The reconstructed displacement–time histories confirm that the system can measure and analyze laser-generated transient surface waves. The established procedure applies directly to subsequent measurements, laying the groundwork for surface-wave velocity measurement, material property evaluation, and defect detection.

1.Lee, C.-K., Wu, W.-J., Wu, G.-Y., Li, C.-L., Chen, Z.-D. and Chen, J.-Y., Design and performance verification of a microscope-based interferometer for miniature-specimen metrology. Optical Engineering, 2005. 44(8): art. 085602.
2.Olmstead, M.A., Amer, N.M., Kohn, S., Fournier, D. and Boccara, A.C., Photothermal displacement spectroscopy: An optical probe for solids and surfaces. Applied Physics A, 1983. 32(3): p. 141-154.
3.Jáuregui, J. and Matthias, E., Thermal diffusivities measured by photodisplacement detection of transient thermal gratings. Applied Physics A, 1992. 54(1): p. 35-39.
4.Rogers, J.A., Dhar, L. and Nelson, K.A., Noncontact determination of transverse isotropic elastic moduli in polyimide thin films using a laser based ultrasonic method. Applied Physics Letters, 1994. 65(3): p. 312-314.
5.Pei, J., Degertekin, F.L., Khuri-Yakub, B.T. and Saraswat, K.C., In situ thin film thickness measurement with acoustic Lamb waves. Applied Physics Letters, 1995. 66(17): p. 2177-2179.
6.Rogers, J.A., Fuchs, M., Banet, M.J., Hanselman, J.B., Logan, R. and Nelson, K.A., Optical system for rapid materials characterization with the transient grating technique: Application to nondestructive evaluation of thin films used in microelectronics. Applied Physics Letters, 1997. 71(2): p. 225-227.
7.Pelivanov, I.M., Kopylova, D.S., Podymova, N.B. and Karabutov, A.A., Optoacoustic method for determination of submicron metal coating properties: Theoretical consideration. Journal of Applied Physics, 2009. 106(1): art. 013507.
8.Wu, G.-Y., Design and construction of innovative laser Doppler vibrometer/interferometer — Measurement of high-performance μ-optomechatronics systems. Ph.D. thesis, Inst. of Applied Mechanics, National Taiwan University, Taipei, Taiwan, 1998.