Düsseldorf 2007 – wissenschaftliches Programm
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Q: Fachverband Quantenoptik und Photonik
Q 30: Poster Nichtlineare optische Effekte und Lichtquellen
Q 30.7: Poster
Dienstag, 20. März 2007, 16:30–18:30, Poster C
The dependence of the Fe Kα yield on the chirp of the femtosecond exciting laser pulse — •Martin Silies1,2, Steffen Linden1,2, Henrik Witte1,2, and Helmut Zacharias1,2 — 1Physikalisches Institut, Westfälische Wilhelms-Universität, Münster — 2Centrum für Nanotechnologie, Münster
The hard x-ray yield generated with femtosecond laser pulses is studied for differently chirped irradiating laser pulses. The radiation of a Ti:sapphire CPA laser system (29 fs, 750 µJ, 1 kHz) is focussed onto a iron containing solid state target producing incoherent hard x-ray radiation, Bremsstrahlung as well as target-specific Kα and Kβ lines. The hard x-ray yield has been optimized by introducing negative and positive group delay dispersion (GDD) and third order dispersion (TOD) to the femtosecond laser pulse. The Kα yield could be enhanced by a factor of 1.7 and reached 1.9·108 Fe Kα photons/s in 4π with the laser pulse positively chirped, and 1.5·108 Fe Kα photons/s in 4π with the pulse negatively chirped. When the pulse energy is lowered to about 400 µJ the yield maximum vanishes and only the maximum at positive chirp remains. We explain the behaviour with induced third order dispersion that led to an asymmetric change of the pulse structure. Furthermore the diameter of the x-ray source has been determined by using a pinhole camera to be about 10 µm (FWHM) and therefore also smaller than the diameter of the applied laser pulse. The diameter of the x-ray source was also independent of the chirp of the laser pulse showing that the expansion of the plasma due to the increased pulse duration is negligible.