Surface and subsurface structure of solids by laser photoacoustic spectroscopy

Abstract

The new technique of photoacoustic spectroscopy is applied to studies of surface and subsurface structures of solids. In the present case, special attention is focused on silicon-nitride ceramic material, which is used for the manufacturing of turbine blades. Good correlation is obtained between the observed photoacoustic signal and surface microstructure. In addition, the photoacoustic signal shows inhomogeneities that are not visually detected under a microscope.

Ultrasonic nondestructive evaluation, microstructure, and mechanical property interrelations

“…Subsurface microstructures of solids have been investigated using photo-acoustic microscopy. i.e., with laser excitation of ultrasonic waves (Wong, et al 1978; Thomas, et al 1980). Microstructure in amorphous as well as polycrystalline solids has been quantitatively characterized with ultrasonic spectroscopy (Gericke, 1970;Brown 1973;Fitting and Adler, 1981).…”

Mesoscopic and Macroscopic Optoacoustic Imaging of Cancer

“…Since its original inception in the 1970s (2), optoacoustic imaging has remained largely an experimental technique. Single detector and single wavelength experimental systems demonstrated aspects of biological imaging in the 90s (3,4), but did not offer features that enabled wide dissemination.…”

Applications of Lockin-Thermography Methods

“…Though this technique was soon extended to imaging [3,4] there were serious restrictions to the size of the sample. Photothermal detection [5] removed this problem, however, it became clear that the depth range needed for many applications required such low modulation frequencies that it took a long time to generate an image.…”