Fast measurement of acoustic dispersion relations based on spatiotemporal phase-contrast imaging

The laser ultrasonics phase-contrast imaging technique is introduced for spatiotemporal acoustic field imaging and quantitative analysis of acoustic dispersion. Two synchronized pulsed Nd:YAG lasers are used as excitation and detection, and an intensified charge-coupled device camera is used to acquire high-resolution spatiotemporal images of Lamb wave propagation in a glass plate. Application of two-dimensional Fourier transform to spatiotemporal data provides dispersion diagrams for identifying distinct Lamb modes, with results showing excellent agreement with theoretical expectations. By combining rapid, full-field data acquisition with high phase sensitivity and intrinsic modal filtering, our approach offers an effective means to characterize acoustic dispersion.