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The author reviews the advances in laser peening without coating (LPwC) technology over the past 30 years in terms of system miniaturization. The development of LPwC began in the early 1990s to prevent stress corrosion cracking (SCC) of in-core components of aged nuclear power reactors. Initial experiments were carried out using a copper vapor laser (CVL), the first high-power, visible-wavelength laser capable of penetrating water without significant energy loss. By reducing the pulse duration from the original tens of nanoseconds to less than 10 nanoseconds, we achieved surface compression without any coating on the material. During this period, non-linear crystal frequency doublers matured and CVLs were replaced by frequency-doubled Nd:YAG lasers. In 1999, LPwC with 200 mJ pulse energy was applied to reactor components to prevent SCC and then moved to fiber delivery technology with 100 mJ laser pulses. Over the last decade, we have developed high-power palmtop-sized lasers that allow us to prototype a portable LPwC system that can be carried as airline baggage. The size and weight are orders of magnitude smaller than conventional systems. We can also operate it outdoors rather than on a vibration-free optical bench in a clean room. This could pave the way for the use of LPwC in the field maintenance of social infrastructure such as bridges, aircraft, construction sites, etc. The principle and effects of LPwC are presented together with recent advances in the portable system.

Bio:
Dr. Yuji Sano is a professor at SANKEN, The University of Osaka, and a program manager (PM) at Institute for Molecular Science (IMS). He is leading a 10-year laser plasma acceleration project funded by the Japanese government (JST-Mirai). His project is developing technologies for laser plasma electron acceleration for FELs, ion acceleration for cancer therapy, and high-power compact lasers for particle acceleration. He has been involved in laser materials processing including laser peening since 1994, and recently developed a portable laser peening (LP) system using a palmtop laser, which expands the application of LP.