Laser-Based Ultrasonics: Applications at APL

onventional ultrasonic techniques have long been recognized for their usefulness in the nondestructive testing of materials and structures. These techniques, based on launching ultrasonic or high-frequency acoustic waves into a material using a coupled transducer, enable the probing of certain material properties. By inducing surface or bulk waves into a material, several material properties, such as thickness, layer structure, and elastic moduli, can be measured. In addition, the material can be checked for cracks, delamination, or changes in porosity. Thus, by launching waves into a material and detecting any corresponding acoustic wave arrivals, it is possible to determine a signifi cant amount of information about the material under test. In contrast to conventional methods, the fi eld of laser-based ultrasonics (LBU) allows the same information to be collected, but through noncontact methods. In this article, we highlight the use of LBU to address problems relevant to air defense, space, and biomedicine.