Abstract. High-speed laser remote sensing of defects inside a concrete specimen was demonstrated. In the proposed measurement setup, high-power laser pulses irradiated a concrete surface to generate vibration that can be detected by an optical interferometer, which was constructed using photorefractive crystal. The laser-based remote sensing system achieved inspection speeds of 25 Hz. The predominant frequency of a mock-up defect that was embedded in a concrete specimen was measured. The inspection result was identical to that obtained using a conventional hammering method.

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We performed simulation experiments to detect defects in a vibrating concrete structure by running loads using a laser differential interferometer. In laser interferometry, it is difficult to acquire vibration information when the amplitude of the out-of-plane vibration is big enough in comparison to the working wave length because the interference signals repeat bright and dark as different frequencies of actual vibrations. In this paper, we performed interference measurements using scattered light from an inspected object as a signal and a reference beam to reduce the relative displacement. Our results show that artificial inner defects in samples under environmental vibration can be detected.

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Laser‐based remote sensing system (LRSS) for detecting defects of concrete lining has been developed. This system can move a central passage in Shin‐kansen tunnel and detected the concrete defects. We have developed automatic positioning and focusing system of impact and detection lasers. It was confirmed that this system inspected concrete defects with remote and high speed and soundness could be judged.