A laser-based remote sensing system (LRSS) for detecting defects in concrete has been
developed. The diffraction efficiency of a photorefractive crystal (PRC) in the LRSS was increased by
an applied electric field. A stabilization system to stabilize the interference pattern in the PRC using the
running hologram technique was constructed. Defects in concrete can be located using initiation and
detection of impact echo and standing Lamb waves (or natural mode of vibration). The prototype of the
LRSS was assembled and set on a small truck. Field experiments were carried out to investigate real
concrete defects of a bridge in bullet-train line in Japan. The LRSS scan concrete surfaces to produce a
two-dimensional map of real concrete defects. The observed predominant frequency of concrete
vibration was consistent with data from impact hammering method.
Keywords: Concrete, photorefractive effect, laser interferometer, homodyne detection, hologram, vibration
detection, Lamb wave, ultrasound, impact echo detection, defect detection.
