A full-field view laser ultrasonic imaging method has been developed that measures acoustic motion at a surface without scanning. Images are recorded at normal video frame rates by using dynamic holography with photorefractive interferometric detection. By extending the approach to ultra high frequencies, an acoustic microscope has been developed that is capable of operation at Gigahertz frequency and micron length scales. Both acoustic amplitude and phase are recorded, allowing full calibration and determination of phases to within a single arbitrary constant. Results are presented of measurements at frequencies of 800-900 MHz, illustrating a multitude of normal mode behavior in electrically driven thin film acoustic resonators. Coupled with microwave electrical impedance measurements, this imaging mode provides an exceptionally fast method for evaluation of electric-to-acoustic coupling of these devices and their performance. Images of 256 240 pixels are recorded at 18 fps rates synchronized to obtain both in-phase and quadrature detection of the acoustic motion. Simple averaging provides sensitivity to the subnanometer level at each pixel calibrated over the image using interferometry. Identification of specific acoustic modes and their relationship to electrical impedance characteristics show the advantages and overall high speed of the technique.

Anisotropic stiffness properties of sheet materials can be determined by measuring the propagation of Lamb waves in different directions, but this typically requires multiple positioning of a suitable transducer at several points or scanning over the area of the sample plate. A laser imaging approach is presented that utilizes the adaptive property of photorefractive materials to produce a real-time measurement of the antisymmetric Lamb traveling wave displacement and phase in all planar directions simultaneously without scanning. Continuous excitation and lock-in methodology is employed, enabling the data to be recorded and displayed by a video camera. Analysis of the image produces a direct quantitative determination of the phase velocity in all directions showing plate stiffness anisotropy in the plane. The method is applicable to materials that scatter light diffusely and provides quantitative imaging of the dynamic surface motion exhibited by traveling elastic waves. A description is given of this imaging process and, for the first time, its ability to perform lock-in measurement of elastic wave displacement amplitude and phase.

An optical photorefractive frequency-domain method is described for measuring displacement amplitude and phase of vibrating surfaces. The method is applicable to diffusely scattering surfaces and usable in either a point-detection or imaging configuration. The method utilizes an optical lock-in approach to measure phase modulation of light scattered from continuously vibrating surfaces. Picometer displacement sensitivities have been demonstrated over a frequency range of 100 Hz to greater than 100 kHz. The response of the spectral method is independent of the vibration frequency above the photorefractive cutoff frequency. Two methods are described that produce a readout beam intensity that is a direct function of the vibration amplitude suitable for imaging.