title: High-harmonic generation by field enhanced femtosecond pulses in metal-sapphire nanostructure.
abstract: Plasmonic high-harmonic generation (HHG) drew attention as a means of producing coherent extreme ultraviolet (EUV) radiation by taking advantage of field enhancement occurring in metallic nanostructures. Here a metal-sapphire nanostructure is devised to provide a solid tip as the HHG emitter, replacing commonly used gaseous atoms. The fabricated solid tip is made of monocrystalline sapphire surrounded by a gold thin-film layer, and intended to produce EUV harmonics by the inter- and intra-band oscillations of electrons driven by the incident laser. The metal-sapphire nanostructure enhances the incident laser field by means of surface plasmon polaritons, triggering HHG directly from moderate femtosecond pulses of ∼0.1 TW cm-2intensities. The measured EUV spectra exhibit odd-order harmonics up to ∼60 nm wavelengths without the plasma atomic lines typically seen when using gaseous atoms as the HHG emitter. This experimental outcome confirms that the plasmonic HHG approach is a promising way to realize coherent EUV sources for nano-scale near-field applications in spectroscopy, microscopy, lithography and atto-second physics.
authors.affiliation: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, South Korea.
authors.forename: Seunghwoi
authors.initials: S
authors.lastname: Han
authors.affiliation: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, South Korea.
authors.forename: Hyunwoong
authors.initials: H
authors.lastname: Kim
authors.affiliation: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, South Korea.
authors.forename: Yong Woo
authors.initials: YW
authors.lastname: Kim
authors.affiliation: School of Mechanical and Aerospace Engineering, Nanyang Technological University (NTU), 50 Nanyang Avenue, Singapore 639798, Singapore.
authors.forename: Young-Jin
authors.identifier: 0000-0002-4271-5771
authors.initials: YJ
authors.lastname: Kim
authors.affiliation: Max Planck Center for Attosecond Science, Max Planck POSTECH/KOREA Res. Initiative, Pohang, Gyeongbuk 376-73, South Korea.
authors.forename: Seungchul
authors.initials: S
authors.lastname: Kim
authors.affiliation: Division of Industrial Metrology, Korea Research Institute of Standards and Science (KRISS), Daejeon 305-340, South Korea.
authors.forename: In-Yong
authors.initials: IY
authors.lastname: Park
authors.affiliation: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, South Korea.
authors.forename: Seung-Woo
authors.initials: SW
authors.lastname: Kim