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TY - CONF AU - Li, C.L. AU - Feng, L. AU - Liu, B. AU - Wang, X.T. AU - Zhang, W.Y. ED - Tavares, Daniel ED - Picoreti, Renan ED - Bruno, Gustavo ED - Marques, Sergio ED - Schaa, Volker R.W. TI - Measurements of Ultraviolet FEL Seed Laser Pulse Width Broading in Thin ß-BBO Crystals J2 - Proc. of IBIC2020, Santos, Brazil, 14-18 September 2020 CY - Santos, Brazil T2 - International Beam Instrumentation Conference T3 - 9 LA - english AB - Short pulse, high power seed lasers have been implemented to improve the longitudinal coherence and shot-to-shot reproducibility of Free Electron Lasers (FEL). The laser pulse duration is typically 100 - 200 fs with wavelengths in the 260 nm range produced from third harmonic generation of a Ti:sapphire laser. The pulse duration must be measured accurately for seeded FEL operation. The Ultraviolet (UV) pulse width measurement can be carried out with intensity cross-correlation based on the difference frequency generation (DFG) in ultrathin ß-Barium Borate (BBO) crystals. The DFG output pulse broadened due to group velocity mismatch between the 266.7 nm and 800 nm components. The broadening effect depends on the BBO crystal thickness so we explored 0.015 mm, 0.055 mm and 0.1 mm thick samples. To the best of our knowledge, this is the first time that ß-BBO crystal with thickness of only 0.015 mm has been used to measure the UV seed laser pulse width. Experiment results show the measured pulse width broadens with increased BBO thickness in agreement with a theoretical model. PB - JACoW Publishing CP - Geneva, Switzerland SP - 140 EP - 144 KW - laser KW - FEL KW - electron KW - polarization KW - free-electron-laser DA - 2020/10 PY - 2020 SN - 2673-5350 SN - 978-3-95450-222-6 DO - doi:10.18429/JACoW-IBIC2020-WEPP20 UR - https://www.jacow.org/ibic2020/papers/wepp20.pdf ER -