Fabrication of tungsten-based optical diffuser using fiberform nanostructure via efficient plasma route.

Optical diffusion is an essential process used to manage photons in a wide range of photoelectric systems. This work proposes an approach to fabricate novel optical diffusers by a plasma-processing technique, using fiberform nanostructures formed by helium plasma irradiation and subsequent annealing. After an annealing procedure in the air for oxidation, the optical properties and the light-diffusing abilities of these nanostructured thin films were studied. In addition to the morphology analysis and total transmittance measurement, the diffusion efficiency of the optical diffusers was analyzed using a transmitted scatter distribution function (TDF). It was revealed that the diffusion efficiency of a device with an irradiation time of 30 minutes could reach 97%. The results demonstrate the potential of these nanostructured optical diffusers for various photoelectric applications.

Enhancement of multi-pulse laser induced damage threshold on Cu mirror under vacuum condition.

Multi-pulse laser induced damage threshold (LIDT) for metallic mirrors are important issue for laser diagnostics in future fusion devices. In this paper, the mechanism of multi-pulse LIDT and the influence of the slip formation and oxidization in atmosphere were investigated experimentally with a Nd:YAG pulse laser whose pulse width and wavelength are ~ 5 ns and 1064 nm, respectively. From detailed surface analysis of laser irradiated part by transmission electron microscopy (TEM), it was found that the miniaturization of crystal size and slip formation were observed on damaged area. Oxidization feature was also revealed from the TEM analysis. It was shown that the multi-pulse LIDT could be increased under vacuum condition compared with that in air atmosphere.

Assessment of multi-pulse laser-induced damage threshold of metallic mirrors for Thomson scattering system.

Multi-pulse laser-induced damage threshold (LIDT) was experimentally investigated up to ~10(6) pulses for Cu, Ag mirrors. The surface roughness and the hardness dependence on the LIDT were also examined. The LIDT of OFHC-Cu decreased with the pulse number and was 1.0 J/cm(2) at 1.8 × 10(6) pulses. The expected LIDT of cutting Ag at 10(7) pulses was the highest; Ag mirror would be one of the best choices for ITER Thomson scattering system. For the roughness and hardness, material dependences of LIDT are discussed with experimental results.

Effect of high-energy neutral particles on extreme ultraviolet spectroscopy in large helical device.

Spectra measured by an extreme ultraviolet (EUV) spectrometer frequently suffer large spike noise when Large Helical Device is operated in low-density range (≤ 3 × 10(13) cm(-3)) with neutral beam injection (NBI). The spike noise completely disappears in electron cyclotron heating discharges. In order to examine the effect of NBI, a carbon filter with thickness of 150 nm was installed in the EUV spectrometer. As a result, the spike noise was reduced by an order of magnitude. It is experimentally verified that the spike noise is caused by escaping high-energy neutral particles resulting from the circulating high-energy hydrogen ions borne from NBI.