title: High harmonic emission from a superposition of multiple unrelated frequency fields.
abstract: We report observations and analysis of high harmonic generation driven by a superposition of fields at 1290 nm and 780 nm. These fields are not commensurate in frequency and the superposition leads to an increase in the yield of the mid-plateau harmonics of more than two orders of magnitude compared to using the 1290 nm field alone. Significant extension of the cut-off photon energy is seen even by adding only a small amount of the 780 nm field. These observations are explained by calculations performed in the strong field approximation. Most importantly we find that enhancement is found to arise as a consequence of both increased ionization in the sum-field and modification of the electron trajectories leading to an earlier return time. The enhanced yield even when using modest intensity fields of 5 x 10(13) Wcm(-2) is extended to the 80 eV range and is a promising route to provide a greater photon number for applications in XUV imaging and time-resolved experiments at a high repetition rate.
authors.affiliation: Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2BW, UK.
authors.forename: T
authors.initials: T
authors.lastname: Siegel
authors.forename: R
authors.initials: R
authors.lastname: Torres
authors.forename: D J
authors.initials: DJ
authors.lastname: Hoffmann
authors.forename: L
authors.initials: L
authors.lastname: Brugnera
authors.forename: I
authors.initials: I
authors.lastname: Procino
authors.forename: A
authors.initials: A
authors.lastname: Zaïr
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Underwood
authors.forename: E
authors.initials: E
authors.lastname: Springate
authors.forename: I C E
authors.initials: IC
authors.lastname: Turcu
authors.forename: L E
authors.initials: LE
authors.lastname: Chipperfield
authors.forename: J P
authors.initials: JP
authors.lastname: Marangos
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D004574:Electromagnetic Fields; D004583:Electrons; D004867:Equipment Design; D007477:Ions; D007834:Lasers; D017711:Nonlinear Dynamics; D016011:Normal Distribution; D055095:Optics and Photonics; D017785:Photons; D010825:Physics / Q000379:methods; D014025:Titanium / Q000737:chemistry
chemical_list: D007477:Ions; D014025:Titanium; D000537:Aluminum Oxide