Frankfurt 2006 – scientific programme
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Q: Quantenoptik und Photonik
Q 55: Nichtlineare optische Effekte und Lichtquellen II
Q 55.11: Talk
Wednesday, March 15, 2006, 16:30–16:45, H14
Enhancement of X-ray Kα flux from a laser-produced plasma by spatio-temporal pulse shaping — •Martin Silies, Tobias Witting, Henrik Witte, and Helmut Zacharias — Physikalisches Institut, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster
The generation of incoherent, but ultrashort Kα radiation by femtosecond laser induced plasmas is based on the action of several highly nonlinear processes. In order to optimize the X-ray yield and to increase the flux in our experiments for time-resolved X-ray diffraction experiments, a closed-loop X-ray optimization set-up with an evolutionary algorithm is assembled. A Ti:sapphire laser pulse with an energy of 600 µ J at 1 kHz repetition rate and a pulse duration of 28 fs is focused by an off-axis parabolic mirror onto a moving metal target in order to produce material specific Kα radiation. An X-ray photodiode monitors the flux of the source and delivers the feedback signal for the closed-loop set-up. This set-up consists of a spatial light modulator for changing the temporal shape of the pulse in combination with a piezoelectric deformable mirror in order to change the spatial profile, both simultaneously controlled by an evolutionary algorithm. With an iterative run with 50 generations each consisting of 30 individuals for both elements the X-ray flux of the source could be enhanced by nearly 50 percent from 8.27· 106 to 1.27· 107 Kα photons per second.