TUOANO01
LBNL, Berkeley, California, USA
SLAC, Menlo Park, California, USA
MIT, Cambridge, Massachusetts, USA
DESY, Hamburg, Germany
AdvR, Inc., Montana, USA
OFS Laboratories, New Jersey, USA
CFEL, Hamburg, Germany
Sub-fs X-ray pulse generation in kilometer-scale FEL facilities will require sub-fs long-term timing stability between optical sources over kilometer distances. We present here key developments towards a completely fiber-coupled, sub-fs optical timing distribution system. Our approach [*] is to lock a femtosecond pulsed laser to a microwave reference and distribute its pulse train through fiber links stabilized by balanced optical cross-correlators (BOCs) [**]. First, we verified that low-noise optical master oscillators for sub-fs timing distribution are available today; the measured jitter for two commercial femtosecond lasers is less than 70 as for frequencies above 1 kHz. Second, we developed a novel 1.2 km dispersion-compensated, polarization-maintaining fiber link to eliminate drifts induced by polarization mode dispersion. Link stabilization for 16 days showed 0.6 fs RMS timing drift and during a 3-day interval only 0.13 fs drift. Lastly, we fabricated a hybrid-integrated BOC using PPKTP waveguides [***] to eliminate alignment drifts and to reduce the link operation power by a factor of 10-100, which will reduce timing errors induced by fiber nonlinearities.
* J. Kim et al., Nat. Photon., 2, 12, 733–736, 2008.
** J. Kim et al., Opt. Lett., 32, 9, 1044–1046, 2007.
*** A. H. Nejadmalayeri et al., Opt. Lett., 34, 16, 2522–2524, 2009.
TUOANO03
SLAC, Menlo Park, California, USA
DESY, Hamburg, Germany
For the generation of ultrashort x-ray FEL pulses, a similarly short, high-brightness electron beam is needed with compression tuned to the extent that a narrow energy spread can still be preserved. Further reduction of the nominal LCLS bunch length by lowering the bunch charge or employing an upstream, emittance-spoiling foil promises to reduce the pulse duration to the level of only a few femtoseconds, presenting a challenge to the temporal resolution of existing longitudinal diagnostics. In answer to this, we have recently commissioned a single-shot, middle-infrared spectrometer for the LCLS. Developed as a robust and cost-effective alternative to other femtosecond-scale beam diagnostics, coherent mid-IR beam radiation measurements and analysis are then employed to probe the LCLS beam just prior to the undulator. Results resolving beam structure to the few-fs level for 20 - 150 pC beams will be presented. Practical design challenges and diagnostic limitations will also be discussed.
DESY Zeuthen, Zeuthen, Germany
INRNE, Sofia, Bulgaria
DESY, Hamburg, Germany
PSI, Villigen PSI, Switzerland
JINR, Dubna, Moscow Region, Russia
RAS/INR, Moscow, Russia
HZB, Berlin, Germany
Chiang Mai University, Chiang Mai, Thailand
MBI, Berlin, Germany
Phys. Rev. ST Accel. Beams 15, 100701 (2012)