title: Bright quasi-phase-matched soft-X-ray harmonic radiation from argon ions.
abstract: Selective enhancement (>10(3)) of harmonics extending to the water window (approximately 4 nm) generated in an argon gas filled straight bore capillary waveguide is demonstrated. This enhancement is in good agreement with modeling which indicates that multimode quasi-phase-matching is achieved by rapid axial intensity modulations caused by beating between the fundamental and higher-order capillary modes. Substantial pulse energies (>10 nJ per pulse per harmonic order) at wavelengths beyond the carbon K edge (approximately 4.37 nm, approximately 284 eV) up to approximately 360 eV are observed from argon ions for the first time.
authors.affiliation: Department of Physics and Astronomy, Queens University Belfast, UK. m.zepf@qub.ac.uk
authors.forename: M
authors.initials: M
authors.lastname: Zepf
authors.forename: B
authors.initials: B
authors.lastname: Dromey
authors.forename: M
authors.initials: M
authors.lastname: Landreman
authors.forename: P
authors.initials: P
authors.lastname: Foster
authors.forename: S M
authors.initials: SM
authors.lastname: Hooker