In this special issue, we present laser techniques applied to maintenance and repair of the social infrastructure such as tunnels, electric power generation and transportation, nuclear facilities. Remote sensing, LIBS, LIDAR, remote technologies coupled with lasers and surface cleaning are reviewed in this issue.

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Laser-based Remote Sensing System (LRSS) for detecting defects in concrete has been developed. That system could run the central passage in the Shinkansen tunnel and detected the concrete defects by laser. And we have developed 50Hz high speed inspection system. Furthermore, we carried out the feasibility study of detecting chemical anchor defects. It was confirmed that soundness can be judged.

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This article introduces a remote laser inspection system that detects cracks on the concrete wall of tunnels. The system consists of three features: distance measurement using an interferometer equipped with a frequency-shifted feedback (FSF) laser, high-speed and high-resolution imaging using a reflected light imaging system, and spectroscopic imaging using triple lasers with different wavelengths. The features have potential to replace conventional manual-based inspection tasks.

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Due to the aging of electric power infrastructure, its maintenance and repair costs are increasing. Therefore, we need a high-performance diagnostic tool to estimate the infrastructure’s degradation condition and its life. Laser-induced breakdown spectroscopy (LIBS) is an attractive tool for the diagnosis of infrastructure because it has several advantages over other analytical methods, such as fast, on-site, and remote measurement of trace elements. In this paper, we explain our recent results on LIBS applications for the diagnosis of electric power infrastructures, such as the quantitative measurement of chlorine concentration distribution in concrete infrastructure, the remote measurement of salt deposition on porcelain insulators, and the remote quantitative measurement of chlorine concentration in salt on stainless steel in a narrow space by simulating the gap between a canister and a concrete body in a concrete cask.

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Big earthquakes and following huge Tsunamis attacked Fukushimadaiichi Nuclear Power Plants at 14:46 on March 11th 2011. And then the plants had severe accidents and released a big amount of radioactive materials to environment through Primary Containment Vessels and Reactor Buildings, and radiation dose revel in the Primary Containment Vessels and Reactor Buildings became extremely higher. In order to reduce operators’ radiation exposure, robots were deployed for emergency response and decommissioning of the plants. Some of the robots equipped with laser range finder to increase operability of the robots. Laser range finder for autonomous control, laser cutting and laser analysis and other laser technologies are desired for future remote operation related to decommissioning of Fukushimadaiichi Nuclear Power Plants. However it is unveiled that there are technical issues to be solved for integration between robotics and Laser technologies.

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Repainting steel surfaces to prevent corrosion is one maintenance method for such large steel structures as old bridges. Unfortunately, the surface preparation process for repainting has workability and environment problems, despite using the highest-grade treatment blasting method. We propose a laser cleaning system using a fiber laser to solve these problems and describe our continuous-wave laser and a circle scan design as key technologies. System safety and standardization are briefly discussed. We introduce the maintenance problems of steel bridges in Japan to show the importance of the installation of our laser device.

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We experimentally detected the inner defects of an underwater concrete structure with a laser method. A concrete sample that includes an artifi cial hollow was placed under water. We irradiated its defect area with a pulsed laser under water and detected a natural vibration that was decided by the size of the defect area. When we irradiated the without-defect area, no natural vibration was detected. This result shows that underwater inspection with a laser method is possible in principle.

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We developed a flash lamp-pumped Nd:YAG laser with 2 J, 50 Hz for a laser-hammering method that inspects tunnel-lining concrete. A simple and compact laser system with a thermal lens effect was compensated by an adjustment of the image tube with high impact resistance and stability. As a result of a 1.5-month outdoor practical test, this laser system was shown to be available for maintenance-free operation.

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