Darmstadt 2008 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 3: Attosecond pulses and high harmonics (jointly with K and Q)
A 3.5: Vortrag
Montag, 10. März 2008, 17:45–18:00, 3C
Formation of Amplitude and Phase during High Harmonic Generation — •Markus Gühr, Brian K. McFarland, Joe P. Farrell, and Philip H. Bucksbaum — Stanford PULSE Center, Stanford University and SLAC, California, USA
High Harmonics of a laser field are generated during the interaction of an intense laser pulse with an atomic or molecular gas. The amplitude and phase of the harmonics contain information about the generation process and the symmetry of the electronic wave functions of the involved atoms or molecules [1].
We measure the amplitude of high harmonics generated in N2 and Ar. Furthermore, we obtain the relative phase between the harmonics from N2 and Ar by interferometric measurements on mixtures of the two gases. We observe phase jumps at the 33rd and the 25th harmonic. The first is accompanied by an amplitude minimum in Ar and attributed to a Cooper minimum. The second is accompanied by an amplitude minimum and a linewidth broadening in N2. It results from the symmetry of the N2 highest occupied molecular orbital.
The discussed phenomena have important implications for the amplitude and phase of attosecond pulses generated via high harmonic generation.
[1] M. Gühr, B. K. McFarland, J. P. Farrell and P. H. Bucksbaum, J. Phys. B: At. Mol. Opt. Phys., 40, 3745-3755 (2007)