There are intense research activities in developing high-power short-wavelength light sources and their application to various fields. This paper describes the overview of the special issue on “recent advances in high-power short-wavelength light sources and their application technology.” The topic of the issue covers the development of deep ultraviolet (DUV) laser diodes, generation of DUV, vacuum ultraviolet (VUV), and extreme ultraviolet (EUV) light by high-order harmonic generation and wave-mixing, and their application, such as laser processing, photoemission spectroscopy, EUV mask inspection, and virus inactivation.

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The development of laser diodes (LDs) in the deep-ultraviolet (UV-C) wavelengths has been progressing rapidly in recent years. Our research group has demonstrated room-temperature continuous lasing of LDs in the 270-nm UV-C wavelength band. This article describes, the key technologies for achieving UV-C LDs: the control of p-type conductivity of AlGaN with high Al composition by polarization doping, and the pseudomorphic growth of AlGaN heterostructure using AlN single-crystal substrates.

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This paper reviews recent advances and challenges in some nonlinear optical borate crystals used for deep ultraviolet light generation. We describe a newly developed large, high-quality CsLiB6O10 (CLBO) crystal and high-power DUV light generation at 266 nm from the frequency quadrupling of a picosecond- pulsed 1064-nm laser. We introduce stable, 10000-hour operation of a 266-nm picosecond laser with an average power of 20 W. We also report achieving an average power of 53 W at 266 nm.

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Argon fluoride (ArF) excimer laser is a typical deep ultraviolet (DUV) light source which can generate above 100-W average power with several tens of nanoseconds pulse duration. Using all-solid-state sub-nanosecond DUV light source as a master oscillator and amplifying by ArF excimer (hybrid ArF laser), both high average power and single transverse mode can be realized. The short pulse hybrid ArF laser generates a burst pulse with individual pulse width of 460 ps. We found that the burst pulse can suppress cracks in non-alkali glass during laser drilling. Multi-hole drilling on non-alkali glass was demonstrated using a diffractive optical element (DOE) at 193 nm. We also demonstrated a laser drilling on 2-mm thick ceramic matrix composite (CMC). Diagonal through holes at the slanted angles of 30° and 20° were created on SiC-CMC.

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Photoelectron spectroscopy is one of the most effective application areas for deep ultraviolet (DUV) and vacuum ultraviolet (VUV) lasers. Angle-resolved photoelectron spectroscopy (ARPES) is widely used in advanced studies of solid-state materials because it can directly probe band structures. We developed a continuous-wave (CW) DUV laser at 213 nm and a picosecond high-repetition-rate VUV laser at 114 nm for ARPES applications. We generated the 213-nm laser by a fourth-harmonic generation with external cavity frequency doublers and generated the 114-nm laser by two-photon resonant four-wave mixing in Xe. Due to the sufficient high photon energies of the lasers, a wide energy range can be measured. CW or high-repetition-rate laser operation reduces the space charge effect and consequently improves the energy resolution of the measurement.

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We have developed some deep ultraviolet laser systems by using fiber lasers and solid-state lasers. These laser systems have been used for laser processing and other scientific applications such as photoemission spectroscopy. Some deep ultraviolet laser systems and their applications are discussed here.

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EUV lithography has been used for high-volume manufacturing of semiconductor devices since 2019. An EUV lithography photomask is a reflection type with Mo/Si multilayer coatings. Since the EUV reflection phase is critical for printability, actinic (at-wavelength) inspection tools and microscopes were developed. In this report, we introduce an EUV specific issue of photomasks and EUV inspection tools for high-volume manufacturing. An EUV microscope is also important for EUV mask development. We made coherent EUV scatterometry microscopes to observe EUV phase images, which captured EUV diffraction from mask patterns without imaging optics. EUV phase images will be helpful for the development of high-contrast EUV masks.

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Ushio have developed 222 nm ultraviolet light source which can inactivates virus effectively similar to harmful spectrum 254 nm. This 222 nm ultraviolet is also understood as much safer than 254 nm. The safety and efficacy have been studied and confirmed in various medical institutes and universities until today as below. This paper presents the characteristics of excimer lamp light sources with a wavelength of 222 nm, their safety and inactivation effects.

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