title: X-ray second harmonic generation.
abstract: We report clear experimental evidence for second harmonic generation at hard x-ray wavelengths. Using a 1.7 Å pumping beam generated by a free electron laser, we observe second harmonic generation in diamond. The generated second harmonic is of order 10 times the background radiation, scales quadratically with pump pulse energy, and is generated over a narrow phase-matching condition. Of importance for future experiments, our results indicate that it is possible to observe nonlinear x-ray processes in crystals at pump intensities exceeding 1016  W/cm2.
authors.affiliation: Physics Department and Institute of Nanotechnology, Bar Ilan University, Ramat Gan 52900, Israel and Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305, USA.
authors.forename: S
authors.initials: S
authors.lastname: Shwartz
authors.affiliation: PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA and Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588, USA.
authors.forename: M
authors.initials: M
authors.lastname: Fuchs
authors.affiliation: The Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Hastings
authors.affiliation: RIKEN SPring-8 Center, Kouto 1-1-1 Sayo, Hyogo 679-5148, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Inubushi
authors.affiliation: RIKEN SPring-8 Center, Kouto 1-1-1 Sayo, Hyogo 679-5148, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: Japan Synchrotron Radiation Research Institute, JASRI, Kouto 1-1-1 Sayo, Hyogo 679-5148, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Katayama
authors.affiliation: PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA and Department of Applied Physics, Stanford University, Stanford, California 94305, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Reis
authors.affiliation: RIKEN SPring-8 Center, Kouto 1-1-1 Sayo, Hyogo 679-5148, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sato
authors.affiliation: Japan Synchrotron Radiation Research Institute, JASRI, Kouto 1-1-1 Sayo, Hyogo 679-5148, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Tono
authors.affiliation: RIKEN SPring-8 Center, Kouto 1-1-1 Sayo, Hyogo 679-5148, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yabashi
authors.affiliation: Physics Department and Institute of Nanotechnology, Bar Ilan University, Ramat Gan 52900, Israel.
authors.forename: S
authors.initials: S
authors.lastname: Yudovich
authors.affiliation: Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Harris