Etsuo Fujiwara

Corrosion resistance of TiN coatings produced by various dry processes

The corrosion resistance of a TiN surface prepared by plasma-based ion implantation (PBII) was compared with that of TiN coating films prepared by sputtering deposition, plasma spraying, and shielded vacuum arc deposition. The corrosion test with the potentiodynamic polarization curve shows that the PBII sample had the best corrosion resistance. The SEM observation indicates that there was no pinhole on the TiN surface prepared by PBII. However, a lot of pinholes were observed in the TiN coating films prepared by the other dry coating processes.

SiO bond breaking in SiO2 by vacuum ultraviolet laser radiation

Abstract Serious optical damage is observed in the surface layer of synthetic quartz glass (SiO2) when it has been used for a high power argon excimer laser operating at 126 nm as a cavity mirror. Microscopic surface observations, XUV reflectivity measurements and XPS analysis show that the damage is mainly ascribed to a photochemical effect. The photochemical effect results in the SiO bond breaking and subsequent crystalline Si isolation in the surface layer.

High-power argon excimer laser at 126 nm pumped by an electron beam

A high-power argon excimer laser has been developed with an output power exceeding 2 MW in the VUV region at 126 nm. As an alternative to a conventional Al/MgF(2)-coated mirror, which was susceptible to damage, an uncoated quartz plate was successfully used as a reflector for reproducible high-power operation of the argon excimer laser without any mirror damage. Observation of the temporal behavior of the laser pulse in relation to that of the gain coefficient is discussed.

Properties of thick DLC films prepared by plasma-based ion implantation and deposition using combined RF and H.V. pulses

Abstract A diamond-like carbon (DLC) film with a thickness of a few μm was prepared on an aluminum alloy by the hybrid process of plasma-based ion implantation and deposition using acetylene gas. The residual compressive stress of the DLC film determined from the substrate curvature decreased with increasing the negative high voltage for ion implantation and was about 0.2 GPa at the high voltage of −20 kV. Ion implantation also served to produce a graded interface between the DLC film and the substrate material. The relaxation of residual stress in the film allowed us to produce thick DLC films of high adhesion. A wear resistance test by the ball-on-disc method showed that the DLC film on an aluminum alloy substrate had the low friction coefficient of about 0.1.

Super-polished silicon carbide mirror for high-power operation of excimer lasers in a vacuum ultraviolet spectral range

We demonstrate the usefulness of a high‐quality SiC mirror for the high‐power operation of vacuum ultraviolet lasers. A void free SiC film of 400‐μm thickness was deposited onto a high‐purity graphite substrate by chemical vapor deposition. The super‐polished SiC mirror, whose surface roughness was 0.2 nm rms, was used as a cavity reflector of a high‐power Ar excimer laser, which operates at 126 nm. The highest output energy of 400 mJ/cm2 per pulse, which corresponds to the energy density of 1 J/cm2 on the SiC mirror surface, has been obtained without any damage to the SiC mirrors.

Surface alterations of SiO2 optics by 9.8 and 8.5 eV laser photons

Abstract Alterations of SiO 2 mirror surfaces, measured by means of surface profiler, reflectance and transmission spectroscopy, and X-ray photoelectron spectroscopy, are reported. The alterations were formed when the mirrors were used as a cavity reflector for Ar and Kr excimer lasers. It is found that Si is enriched in the surface layers which were exposed to 9.8 eV photons from the Ar excimer laser. The Kr excimer laser photons, the energy of which is 8.5 eV, do not induce such a phenomenon. The Ar excimer laser photons, surmounting the fundamental band gap of SiO 2 , 9 eV, are assumed to create a high density of excitons that induce SiO breaking, resulting in silicon enrichment and oxygen depletion. The Si enrichment is observed for both glassy and crystalline SiO 2 .

A preliminary study on laser-triggered lightning

As a preliminary study on triggering lightning with a CO2 high-power laser, we carried out laser-triggered discharge experiments to investigate the necessary conditions for initiating and guiding an electrical streamer with a CO2 laser-produced plasma channel. We found the following. (1) The necessary electric field for initiating a streamer with the plasma channel depends closely on the absorbed energy for producing the plasma channel and not on the length of the plasma channel. The higher the absorbed energy, the smaller the necessary electric field. The minimum electric field is about 200 kV/m. (2) The necessary electric field for guiding a streamer by the plasma channel is lower than that for initiating a streamer. The minimum electric field is about 170 kV/m. Furthermore, we observed the electric field at the top of a 50-m tower and the field on the ground simultaneously during 10 Japanese winter thunderstorms. The observed results agree with theoretical calculations showing that the field at the top of a 50-m tower is on average 2 orders larger than the field on the ground. We conclude that it is highly possible to trigger a lightning discharge if we shoot a CO2 laser-produced plasma channel upward through the top of a high grounded tower under conditions of high thunderstorm electric fields.

Tunable oscillation of a high-power argon excimer laser in the vacuum-ultraviolet spectral region

Successful oscillation of a tunable, high-power argon excimer laser is reported. The wavelength was tuned from 124.5 to 127.5 nm with a spectral width of 0.3 nm. The output power of 2.2 MW, obtained at the line center, is 3 orders of magnitude larger than the value reported previously by Wrobel et al. [Appl. Phys. Lett. 36, 113 (1980)]. The possibility of frequency conversion of the argon excimer laser radiation to other wavelengths by a stimulated Raman scattering process is discussed.

Surface Modification of High-Speed Tool Steel by Repeated Irradiations of Intense Pulsed Ion Beam

Surface modification of a high-speed tool steel (SKH51) has been performed by irradiation of the proton intense pulsed ion beam (IPIB) with the ion energy of 180 keV, the ion current density of 460 A/cm2, and pulse duration of 65 ns. By 1-pulse irradiation of the IPIB, the second phase carbides such as VC, Fe6C, and Cr6C are dispersed from the irradiated surface, and the average grain size decreases to 240 nm corresponding to approximately 1/30 of the untreated one. Repeated irradiations of the IPIB result in the reduction in grain size and conversion of an α-Fe structure to a γ-Fe one. The SKH51 treated by 10-pulses irradiation has a single phase of γ-Fe, and the grain size is reduced to approximately 1/170 of that of the untreated one. In addition, the 10-pulses-irradiated surface has an improved wear resistance.

Profile of implanted nitrogen ions in Al alloy for mold materials

Abstract Nitrogen ions were implanted into an aluminum alloy (Al-7Si) for casting mold materials by plasma-based ion implantation to enhance wear resistance and hardness of the target. A negative high-voltage pulse of 10 kV with a pulse width of 10 μs and repetition rate of 100 Hz was applied to the target immersed in the nitrogen plasma produced by filament discharge. Auger electron spectroscopy (AES) analysis indicated that the depth profile of implanted nitrogen had two peaks, corresponding to N + and N 2 + ions, for short implantation times less than approximately 30 min. For implantation times longer than 30 min, however, the two peaks merged with each other. The AES analysis also indicated the formation of AlN by implantation of nitrogen ions. The AlN was formed in the surface region within the nitrogen ion range. A wear-resistance test by the ball-on-disc method showed that nitrogen ion implantation resulted in a reduction of the friction coefficient from 0.6 to 0.1 and the wear resistance was increased by one order of magnitude. It was also found that nitrogen ion implantation enhances the hydrophilic properties.