Near-field scanning laser source technique and microfabricated ultrasound receiver

The scanning laser source (SLS) technique has been proposed recently as an effective way to investigate small surface-breaking defects. We now propose an extension of the SLS approach to map surface-breaking defects by bringing both the source and the receiver to the near-field scattering region of the defects. For the purpose of near-field ultrasound measurement, silicon microcantilever probes are fabricated and their acoustical characteristics are investigated. The fundamental frequency of the microcantilever is measured and compared with analytically calculated fundamental frequency. The performance of the fabricated microcantilevers as ultrasound detectors is investigated. Broadband ultrasound is generated by a laser source and the resulting surface acoustic displacements are monitored using the microcantilever probe in the near-field of the source. Both the laser-generated ultrasonic source and the microcantilever probe are used to monitor near-field scattering by a surface-breaking defect.