We demonstrate the control of high-harmonic generation in a hollow fiber by shaping the spatial structure of the generating laser pulse. We use a liquid-crystal-based two-dimensional spatial light modulator to control the spatial phase of the driver pulse. An evolutionary algorithm finds the spatial laser phase distribution that is optimal for reaching maximum total harmonic yield and for selectively enhancing the cutoff region of the spectrum. We show that enhacement of harmonic generation is related to coupling into a single fiber mode. Our results directly show that spatial properties of the laser are important parameters in fully controlling the high-harmonic spectrum. It is thus not possible to derive the controllability of the high-harmonic generation from the single-atom response only.
© 2005 Optical Society of America
(190.2620) Nonlinear optics : Harmonic generation and mixing
(190.4160) Nonlinear optics : Multiharmonic generation
(190.7110) Nonlinear optics : Ultrafast nonlinear optics
(300.6560) Spectroscopy : Spectroscopy, x-ray
(320.5540) Ultrafast optics : Pulse shaping
Thomas Pfeifer, Ron Kemmer, Robert Spitzenpfeil, Dominik Walter, Carsten Winterfeldt, Gustav Gerber, and Christian Spielmann, "Spatial control of high-harmonic generation in hollow fibers," Opt. Lett. 30, 1497-1499 (2005)