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MO: Fachverband Molekülphysik
MO 18: Experimentelle Techniken
MO 18.7: Talk
Thursday, March 5, 2009, 12:15–12:30, VMP 6 HS-F
Determination of the absolute photon flux of femtosecond VUV pulses from high harmonic generation with a Gas Monitor Detector — •Torsten Leitner1, Philippe Wernet1, Kai Godehusen1, Olaf Schwarzkopf1, Tino Noll1, Jerome Gaudin3, Andrei Sorokin2, Henrik Schoeppe2, Mathias Richter2, and Wolfgang Eberhardt1 — 1Helmholtz-Zentrum Berlin - Elektronenspeicherring BESSY II — 2Physikalisch-Technische Bundesanstalt - Berlin — 3DESY/ European XFEL Project Team - Hamburg
The generation of high-order harmonics of femtosecond lasers in rare gas media has recently emerged as a promising tool to produce bright atto- and femtosecond vacuum-ultraviolet (VUV) and soft x-ray pulses. One of the key parameters of a light source is its photon flux. A suitable tool for counting VUV photons is provided by a Gas Monitor Detector, wherein the number of rare gas ions generated by the passing VUV beam is counted. Knowing the exact gas pressure inside the detector and the wavelength of the light one can translate the absolute number of ions into absolute photon numbers. The detector works within a range of peak irradiances from 10−2 Wcm−2 (BESSY II) up to 1011 Wcm−2 (FLASH). Such a device, developed and calibrated by the PTB was used to measure the absolute number of photons generated at the BESSY High-order Harmonic Generation source. Additionally, the photon flux was estimated from the photo-current of a calibrated GaAsP diode. A comparison of both measurements proofed, that the diode allows for a good approximation of the number of photons within an error of 20% even for pulses as short as several tens of femtoseconds.