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Spatially resolved acoustic spectroscopy (SRAS) is a non-destructive acoustic microscopy microstructural-crystallographic characterization technique commonly used in the study of crystalline or polycrystalline materials. The technique can provide information about the structure and crystallographic orientation of the material. Traditionally, the information provided by SRAS has been acquired by using diffraction techniques in electron microscopy.

Laser ultrasound

In a SRAS measurement two lasers are used, one for the generation of acoustic waves and one for the subsequent detection of these waves.

An optical amplitude grating, illuminated by the generation laser, is imaged onto the specimen surface. The incident light is thermoelastically absorbed, creating surface acoustic waves, such as Rayleigh waves.

Microstructure imaging

The velocity of acoustic waves in a material is a function of many essential

Orientation mapping

Having measured the SAW velocity in multiple directions the challenge is then to convert this information into the measurement of crystallographic orientation. The direct calculation of the orientation from velocity is a difficult problem. However, the numerical calculation of the SAW velocity as a function of SAW velocity is relatively simple, as first outlined by Farnell. Therefore, a database of possible slowness surfaces can be pre-calculated and compared to the measurement values.