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Development of high-energy and high repetition rate compact pulse laser system for inspection of tunnel concrete (Conference Presentation)
Author(s): Hajime Okada; Noboru Hasegawa; Katsuhiro Mikami; Toshiyuki Kitamura; Shuji Kondo; Masaharu Nishikino; Tetsuya Kawachi
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Paper Abstract

A simplified flash-lamp pumped high-average-power Nd:YAG Q-switched laser system based on a master oscillator power amplifier platform was developed toward outside laser remote sensing. The performance of the laser system was demonstrated, obtaining 4.7 J output pulse energy with a 50 Hz operating frequency on the optical breadboard of 1.8 m x 0.7 m size. The pulse energy from master oscillator was approximately 250 mJ with 14 ns pulse duration that was amplified by first Nd:YAG rod crystals with double pass amplification. Then, output laser pulse from first YAG rod was amplified by second and third Nd:YAG rod crystals. The beam pattern was image relayed using lens pair between all Nd:YAG rods to maintain the good beam spatial profile in rod amplifiers to avoid the optical damages induced by non-uniform beam profile. The focal lengths of thermal lens effect in each Nd:YAG rod crystal was about 2 m that were compensated by an adjustment of lens pairs. The amplified pulse laser was focused using focusing lens pair on the concrete surface to generate panel vibrations by laser ablation and/or thermal stress, acting thus as a hammer. The focal length of lens pair was approximately 7 m that is assumed the typical a tunnel roof in Japan. The energy transfer efficiency from final amplifier to concrete surface was approximately 87%, its main reason of reduction of efficiency was beam quality of master oscillator. That efficiency was 89% with only oscillator beam.

Paper Details

Date Published: 14 March 2018
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Proc. SPIE 10511, Solid State Lasers XXVII: Technology and Devices, 105110U (14 March 2018); doi: 10.1117/12.2291157
Show Author Affiliations
Hajime Okada, National Institutes for Quantum and Radiological Science and Technology (Japan)
Noboru Hasegawa, National Institutes for Quantum and Radiological Science and Technology (Japan)
Katsuhiro Mikami, National Institutes for Quantum and Radiological Science and Technology (Japan)
Toshiyuki Kitamura, National Institutes for Quantum and Radiological Science and Technology (Japan)
Shuji Kondo, National Institutes for Quantum and Radiological Science and Technology (Japan)
Masaharu Nishikino, National Institutes for Quantum and Radiological Science and Technology (Japan)
Tetsuya Kawachi, National Institutes for Quantum and Radiological Science and Technology (Japan)


Published in SPIE Proceedings Vol. 10511:
Solid State Lasers XXVII: Technology and Devices
W. Andrew Clarkson; Ramesh K. Shori, Editor(s)

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