Seeing through opaque materials with light: advances in adaptive photodetectors for laser based ultrasound sensing

Beyond traditional communication needs, coherent detection systems are finding new applications in the areas of industrial inspection, phase-locking of free-running lasers, and spectral analysis. An example of the former includes laser-based ultrasound, where laser beams replace conventional mechanical transducers to both generate and sense ultrasound, enabling one to, in essence, image through opaque materials with light. Such noncontact remote diagnostics have application to manufacturing process control and in-field inspection of metallic, semiconductor and advanced composite materials.