title: Direct observation of laser filamentation in high-order harmonic generation.
abstract: We investigate the spatial evolution of a laser pulse used to generate high-order harmonics (orders ranging from 45 to 91) in a semi-infinite helium-filled gas cell. The 5 mJ, 30 fs laser pulses experience elongated focusing with two distinct waists when focused with f/125 optics in 80 Torr of helium. Extended phase matching for the generation of harmonics occurs in the region between the double foci of the laser, where the laser beam changes from diverging to converging.
authors.affiliation: Department of Physics and Astronomy, Brigham Young University, Provo, UT 84602, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Painter
authors.forename: Mark
authors.initials: M
authors.lastname: Adams
authors.forename: Nicole
authors.initials: N
authors.lastname: Brimhall
authors.forename: Eric
authors.initials: E
authors.lastname: Christensen
authors.forename: Gavin
authors.initials: G
authors.lastname: Giraud
authors.forename: Nathan
authors.initials: N
authors.lastname: Powers
authors.forename: Matthew
authors.initials: M
authors.lastname: Turner
authors.forename: Michael
authors.initials: M
authors.lastname: Ware
authors.forename: Justin
authors.initials: J
authors.lastname: Peatross