title: Efficient high-order harmonic generation boosted by below-threshold harmonics.
abstract: High-order harmonic generation (HHG) in gases has been established as an important technique for the generation of coherent extreme ultraviolet (XUV) pulses at ultrashort time scales. Its main drawback, however, is the low conversion efficiency, setting limits for many applications, such as ultrafast coherent imaging, nonlinear processes in the XUV range, or seeded free electron lasers. Here we introduce a novel scheme based on using below-threshold harmonics, generated in a "seeding cell", to boost the HHG process in a "generation cell", placed further downstream in the focused laser beam. By modifying the fundamental driving field, these low-order harmonics alter the ionization step of the nonlinear HHG process. Our dual-cell scheme enhances the conversion efficiency of HHG, opening the path for the realization of robust intense attosecond XUV sources.
authors.affiliation: Department of Physics, Lund University, P O Box 118, SE-22100 Lund, Sweden.
authors.forename: F
authors.initials: F
authors.lastname: Brizuela
authors.forename: C M
authors.initials: CM
authors.lastname: Heyl
authors.forename: P
authors.initials: P
authors.lastname: Rudawski
authors.forename: D
authors.initials: D
authors.lastname: Kroon
authors.forename: L
authors.initials: L
authors.lastname: Rading
authors.forename: J M
authors.initials: JM
authors.lastname: Dahlström
authors.forename: J
authors.initials: J
authors.lastname: Mauritsson
authors.forename: P
authors.initials: P
authors.lastname: Johnsson
authors.forename: C L
authors.initials: CL
authors.lastname: Arnold
authors.forename: A
authors.initials: A
authors.lastname: L'Huillier