Photoacoustics, or laser-generated ultrasonic pulses in solid or liquid media, have been used for years in nondestructive testing, process monitoring and materials characterization. Researchers from Northwestern University in Evanston, Ill., have described several improvements that may increase their suitability for nondestructive testing and biomedical applications such as laser-generated ultrasound.

In the Aug. 1 issue of Applied Optics, they describe several sources consisting of a laser pulsed through a fiber optic cable to a generation head. The generation head in all cases was coated with a ~0.2-mm layer of dried graphite suspension, which exhibited the criteria for an efficient light-absorbing target. Rapid thermoexpansion of the graphite transmitted ultrasound into various media, and the researchers developed several ultrasound radiation patterns based on the angle of the graphite layer to the incident laser beam. Furthermore, they developed two catheter-based photoacoustic probes by combining a photoacoustic source and a fiber optic ultrasound receiver, and tested its effectiveness on the inner walls of water-filled tubes made of various materials.