title: Investigation of ablation thresholds of optical materials using 1-µm-focusing beam at hard X-ray free electron laser.
abstract: We evaluated the ablation thresholds of optical materials by using hard X-ray free electron laser. A 1-µm-focused beam with 10-keV of photon energy from SPring-8 Angstrom Compact free electron LAser (SACLA) was irradiated onto silicon and SiO2 substrates, as well as the platinum and rhodium thin films on these substrates, which are widely used for optical materials such as X-ray mirrors. We designed and installed a dedicated experimental chamber for the irradiation experiments. For the silicon substrate irradiated at a high fluence, we observed strong mechanical cracking at the surface and a deep ablation hole with a straight side wall. We confirmed that the ablation thresholds of uncoated silicon and SiO2 substrates agree with the melting doses of these materials, while those of the substrates under the metal coating layer are significantly reduced. The ablation thresholds obtained here are useful criteria in designing optics for hard X-ray free electron lasers.
authors.affiliation: Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan. koyama@spring8.or.jp
authors.forename: Takahisa
authors.initials: T
authors.lastname: Koyama
authors.forename: Hirokatsu
authors.initials: H
authors.lastname: Yumoto
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Senba
authors.forename: Kensuke
authors.initials: K
authors.lastname: Tono
authors.forename: Takahiro
authors.initials: T
authors.lastname: Sato
authors.forename: Tadashi
authors.initials: T
authors.lastname: Togashi
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Inubushi
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Katayama
authors.forename: Jangwoo
authors.initials: J
authors.lastname: Kim
authors.forename: Satoshi
authors.initials: S
authors.lastname: Matsuyama
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Mimura
authors.forename: Makina
authors.initials: M
authors.lastname: Yabashi
authors.forename: Kazuto
authors.initials: K
authors.lastname: Yamauchi
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Ohashi
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ishikawa