title: Wavelength scaling of high harmonic generation close to the multiphoton ionization regime.
abstract: We study the wavelength scaling of high harmonic generation efficiency with visible driver wavelengths in the transition between the tunneling and the multiphoton ionization regimes where the Keldysh parameter is around unity. Our experiment shows a less dramatic wavelength scaling of efficiency than the conventional case for near- and mid-IR driver wavelengths, and it is well explained by a generalized three-step model for increased Keldysh parameters that employs complex ionization times in addition to the nonadiabatic ionization. The complex ionization time is critical to avoid the divergence when replacing the quasistatic ionization model by the more general nonadiabatic ionization model. Together, the two modifications present a consistent description of the influence of the atomic potential on the rescattering process in the intermediate Keldysh regime.
authors.affiliation: Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts 02139, USA. cjlai@mit.edu
authors.forename: Chien-Jen
authors.initials: CJ
authors.lastname: Lai
authors.forename: Giovanni
authors.initials: G
authors.lastname: Cirmi
authors.forename: Kyung-Han
authors.initials: KH
authors.lastname: Hong
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Moses
authors.forename: Shu-Wei
authors.initials: SW
authors.lastname: Huang
authors.forename: Eduardo
authors.initials: E
authors.lastname: Granados
authors.forename: Phillip
authors.initials: P
authors.lastname: Keathley
authors.forename: Siddharth
authors.initials: S
authors.lastname: Bhardwaj
authors.forename: Franz X
authors.initials: FX
authors.lastname: Kärtner