Laser acceleration technology is expected to contribute to the miniaturization of particle accelerators because the acceleration gradient is orders of magnitude steeper than that of conventional RF accelerators. In this special issue, we collected review papers on laser acceleration of electrons and ions as well as the development of high-intensity laser technologies necessary for stable operation of laser accelerators. We hope that this special issue will provide useful information for researches and engineers who are interested in laser acceleration.

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Laser wakefield acceleration (LWFA) research has been conducted mainly for basic science which include understanding acceleration mechanism in relativistic plasma, but it is now shifting to the research for realization of laser-driven accelerators. In this paper, we introduce the current status of LWFA research aimed at demonstrating laser-driven X-ray free electron laser (XFEL) under MIRAI-program at RIKEN Harima campus, and outline the current status of research and development toward the stable LWFA accelerator for practical use.

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We introduce a research field in which coherent, x-rays (including extreme-ultraviolet light) are generated based on a free-electron laser (FEL) using laser-plasma electron acceleration. A brief formulation of the self-amplified spontaneous emission (SASE) FEL is given and the required electron beam parameters for an SASE FEL in the X-ray region are discussed. We also present experimental activities in the world and simulation modeling.

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The laser-driven dielectric accelerator may become a good candidate for the next generation accelerator since it can realize both of high gradient and multi-bunch high current accelerator. However we still have many issues including the output power, the accelerating gradient and the total conversion efficiency. We will introduce some typical methods of the dielectric accelerator and those technical issues.

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Energetic ion beams are generated from the plasma produced by the interaction between high intensity PW-class laser and solid density targets. Because of the unique features of the beam, it attracts many fields of applications, thus active research is carried out all over the world for aiming at the generation of better quality beam. Here we introduce one of the recent achievements in the laser-driven ion acceleration research, especially investigation of the mechanisms of the heavy ion acceleration and the attempt to establish the laser-driven carbon injector for the medical accelerator.

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The development of laser-driven neutron source (LDNS) utilizing laser-accelerated ions and its application to several kinds of neutron analysis were performed at LFEX facility of ILE Osaka University. The LDNS generates neutrons having wide range of energies from meV to MeV. The main argument of this review is to demonstrate “Single-Shot” neutron analysis by LDNS, where one analysis is accomplished by a single bunch of neutrons generated with a single laser shot. This method enables the high-speed analysis of nuclear information including elements and isotopes.

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We demonstrate a new scheme using the prominent characteristics of micron-scale hydrogen cluster targets for achieving a level of 0.3 GeV quasi-monoenergetic proton bunch acceleration with low angular divergence by utilizing the internal degree of freedom. In this scheme, the collisionless shock dynamics inside the micron-scale cluster are subsequently coupled with the relativistically induced transparency effect of a high-intensity laser. This step plays an important role. The scheme, which stably works for the finite ranges of parameters with threshold values, is available for experiments.

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High-average-power femtosecond lasers with petawatt peak powers are essential for the practical achievement of such new technologies as laser-driven accelerators. To achieve a high repetition rate petawatt laser, a high repetition rate, high pulse energy laser of diode-pumped solid-state laser with pulse energy of 100 J and repetition rate of 100 Hz is required as a pump source. In this paper we review the world’s trends of high repetition rate, high pulse energy laser of diode-pumped solid-state laser and the current progress on development a diode-pumped conduction-cooled low-temperature Yb:YAG active mirror laser.

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Compact, powerful lasers will bring great benefit in cutting-edge science and technology. The recent progress of micro solid-state photonics offers tremendous effects in the downsizing of power lasers. Such extremely high-brightness lasers will enable new sciences, including laser-driven electron accelerators, toward a table-top X-ray free electron laser (XFEL) based on laser plasma acceleration (LPA) and THz wave dielectric laser acceleration (THz-DLA). These tiny integrated lasers are also promising for the future of high-field laser industrial, bio-medical, and safety applications as well as infrastructure maintenance for subsequent innovations.

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The Telescope Array (TA) project focuses on Ultra-High Energy Cosmic Ray (UHECR) observations. TA observes the fluorescence of nitrogen excited by secondary cosmic rays with a telescope (fluorescence detector: FD). The influence of atmospheric transparency in the propagation process must be considered from the point of its occurrence to FD when analyzing cosmic rays. A bistatic-LIDAR facility was constructed for TA experiments to estimate the inhibition of fluorescence propagation by aerosols. This facility is called the Central Laser Facility (CLF). In this paper, we discuss the relative analysis method of bistatic-LIDAR. The optical thickness of aerosol by this analysis method can be obtained by the numerical value (VAOD) integrated up to an arbitrary surface altitude in the vertical direction. Following previous research, this paper records VAOD up to an altitude of 5 km, and the median and distribution widths in 2015 were 0.042+0.031 −0.014 . We also compared our result with Mie-LIDAR from another year (a previous experiment) and confirmed that the values are consistent.

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We developed 222 nm-UVC lamps for disinfection in occupied space. Since these lamps require an operation lifetime of several thousand hours, such critical characteristics as radiation spectra must be investigated after long-term operation. In this study, we investigated the output, spectral changes, and filtering characteristics after long-term operation of filtered 222 nm-UVC lamps and confirmed just minimal changes in the lamp spectrum even with continuous operation over 8000 h. We found no changes in the harmful ultraviolet ratio: 235 ~ 320 nm integrated intensity/200 ~ 230 nm integrated intensity. Lifetime tests continue, and a longer life expectancy is expected. We also explained the light distribution and dimming functions of next-generation lamps. This new source has a wider light distribution, and dimming will enable continuous operation. We anticipate that this will allow more effective infection control.

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