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Overview of the principle setup of the TEO experiment. The relative arrival time between FEL pulse and IR pulse is measured inside the accelerator tunnel using the electron bunches instead of the XUV pulses.
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For two-colour pump-probe experiments carried out at the freeelectronlaser FLASHat DESY, theXUV FEL laser pulses must be synchronizedwith femtosecondprecision to optical laser pulses (120fs, 20 μJ Ti:Sapphire). An electro- optical (EO) sampling diagnostic measures the arrival time jitter of the infrared pump-probe laser pulse with respect to the el...
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... of ≈ 60 fs RMS of the photon pulse arrival-time. The IR laser system is located in a laser laboratory at the end of the FEL linear accelerator in close vicinity to the pump-probe experiments. To transport the laser pulse Fourier limited to the location of TEO in the accelerator tunnel, which is located 160 m away from the laser lab- oratory (see fig. 1). The laser pulse transport system is the most complex part of the TEO experiment, because the dispersion of 160 m bulk glass fibre has to be recom- pressed accurately. Additionally the fibre length is modu- lated by thermal expansion and micro-phonics, which has to be compensated by active path length stabilization. A detailed ...
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Citations
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Laser-based diagnostic systems play an increasingly im- portant role in accelerator diagnostics in, for instance, elec- tron bunch length measurements. To date, the laser sys- tem of choice for electro-optic experiments has been the Ti:sapphire laser, providing several nanojoules of pulse en- ergies at fixed a repetition rate, which is not well suited to the bunch structure of accelerator facilities such as FLASH. Limited long-term stability and operability of Ti:sapphire systems are significant drawbacks for a continuously run- ning measurement system requiring minimal maintenance and maximum uptime. We propose fiber lasers as a promis- ing alternative with significant advantages. Gating of the pulse train to match the bunch profile is simple with fiber- coupled modulators, in contrast to bulk modulators needed for Ti:sapphire lasers. An in-line fiber amplifier can boost the power, such that a constant pulse energy is maintained regardless of the chosen pulse pattern. Significantly, these lasers offer excellent robustness at a fraction of the cost of a Ti:sapphire laser and occupy a fraction of the optical table space.
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