Effect of hydrogen and helium irradiation on optical property of tungsten

Tokunaga, Kazutoshi*; Ezato, Koichiro; Suzuki, Satoshi; Akiba, Masato; Fujiwara, Tadashi*; Yoshida, Naoaki*

Polycrystalline tungsten samples have been irradiated by 19 keV pulsed hydrogen and helium beam up to 110/m. Optical reflectivity has been measured with an ultraviolet-visible and near-infrared spectrophotometer, and a Fourier transform-infrared (FT-IR) spectrometer for the wave length between 190 - 2400 nm, 1.4 - 20 m, respectively. In addition, optical constants have been calculated by results measured using a spectroscopic ellipsometer. Surface morphology has been also examined with a scanning electron microscope. Loss of metallic gloss and remarkable reduction of reflectivity (190-2400 nm) occurs by the hydrogen and helium irradiation of 1022 He/m. In particular, helium beam irradiation at a peak temperature 2600 C causes remarkably decrease of the reflectivity due to fine uneven morphology and bubble formation near-surface. The reduction of the reflectivity is considered to be mainly due to the porous structure with nano-scale hydrogen and helium bubbles.