Limits to the detection of small internal voids in solids with holographic techniques.
The ability to find small voids in acoustically excited solid specimens using coherent optical detection methods is limited by three factors: available ultrasonic power levels; noise elements; and nonlinear properties of the working materials. Detection sensitivity constraints due to power limitations are established here. A void embedded in an elastic half-space is used as a physical model. Free surface deformations due to internal void-scattered ultrasonic waves are computed for select cases. Deformations are too small for direct optical measurement. Deflections of a liquid layer free surface above the elastic halfspace represent an amplified copy of the elastic boundary deformation and improved detection sensitivity. Holographic techniques with noise reduction features to observe the liquid surface profile are discussed.
Pernick
B J
BJ