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Fiber-optic photoacoustic sources for nondestructive testing and biomedical applications are described. The photoacoustic sources consist of a pulsed laser, a fiber-optic cable, and a generation head. The generation head is a miniature hermetically sealed chamber, which can be embedded into solid structures or immersed in liquid media. The face of the chamber acts as a target for laser irradiation. Bulk ultrasonic waves generated inside of the target are transmitted into the medium. The proposed systems offer wide ultrasonic range (0.5-15 MHz), easy control over directivity of the ultrasonic beam, high efficiency of generation, and the ability to operate in a harsh environment. Sources with different radiation patterns with respect to the optical axis of the fiber, such as normal, sideways, as well as focused, have been devised. We present a proof-of-concept experiment using these sources in combination with fiber-optic ultrasonic receivers.

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A laser ultrasonic system for real-time cure monitoring of a graphite-epoxy composite is proposed. The system contains an array of fiberized laser ultrasonic sources, and an embedded fiber optic Sagnac ultrasonic sensor, and is integrated with a Resin Transfer Molding machine. The use of an optical switch allows ultrasonic generation at several locations of the composite part. Ultrasound generated by the laser source is transmitted into the composite and is detected by the embedded sensor. The cure state is inferred from measurements of ultrasonic velocity. The results of ultrasonic measurements during manufacturing of a composite specimen are presented. The laser ultrasonic cure monitoring system described in this paper has the ability tooperate in a high temperature and high pressure environment; is small enough to be incorporated into molds; and measures the cure state at several locations within the composite part.