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EO systems at the DESY VUV-FEL

EO systems at the DESY VUV-FEL. Stefan Düsterer for the VUV - FEL Team F. Van den Berghe, J. Feldhaus, J. Hauschildt, R. Ischebeck, K. Ludwig, H. Schlarb , B. Schmidt, S. Schmüser, S. Simrock, B. Steffen, A. Winter and all the others

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EO systems at the DESY VUV-FEL

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  1. EO systems at the DESY VUV-FEL Stefan Düsterer for the VUV - FEL Team F. Van den Berghe, J. Feldhaus, J. Hauschildt, R. Ischebeck, K. Ludwig, H. Schlarb, B. Schmidt, S. Schmüser, S. Simrock, B. Steffen, A. Winter and all the others Adrian Cavalieri, David Fritz, Soo-Heyong Lee, David Reis (Michigan University Ann Arbor, Michigan)

  2. pump-probe fs-laser for FEL-experiments TiSa fs-oscillator EOS „Electro Optical Sampling“ chirped laser pulse TEO „Timing Electro Optical sampling“ 45° - geometry The 2 EOS systems Experiments

  3. delay delay + jitter TimingEO Timing monitor for the FEL-optical pump-probe Experiments • optimized for electron bunch ARRIVAL TIME measurements • part of the pump-probe laser system • final goal: provide timing data to users

  4. FEL pulse Optical pulse to TEO Layout: pump-probe experiments optical laser

  5. TEO Pockels cell 50 % beam splitter

  6. TEO The laser hutch overview picture - CDR layout

  7. The TEO layout - in the laser hutch laser hutch - CDR layout

  8. tunnel - CDR layout High degree of automation 19 motors 6 cameras 3 photo diodes / PMTs every important parameter can be controlled and changed from the control room - fully integrated in the control system - The TEO layout - in the tunnel

  9. TEO - first steps... Laser hutch Accelerator tunnel

  10. TEO - simulations critical parts like the compressor the phase-shaper the imaging of the crystal the interaction between laser and el. field in the crystal were simulated in order to optimize TEOs performance

  11. introducing LAB II simulation software • Simulation of fs-pulse propagation by Th. Feurer and group (Jena / MIT /Bern) • time - frequency domain (no spatial calculations) • linear and nonlinear effects / three wave mixing • various materials • compressors, strechers and phase shaper • auto- / cross-correlation, FROGs • and much much more Free download at www.lab2.de Based on LabView

  12. ~ 70 fs FWHM Lab II - simulation of TEO

  13. The compressor compensate for dispersion induced fs-pulse broadening by the 170 m glass fiber compensates the huge Group Velocity Dispersion (GVD) (second order deriv. of phase) BUT induces third (and higher) order phase distortions (TOD) TOD induced by fiber: 0.5 107 fs3 / TOD by compressor: 1-2 107 fs3

  14. folding mirror the phase shaper - actual design Geometry is entirely on-axis. ( design by G. Stobrawa, U. Jena) • algorithms for LCD-matrix • - start with genetic algorithm (Soo / Michigan) • next step: • parameterization with to Taylor coefficients . of the phase (about 100 times faster - Jena)

  15. ray tracing well below diffraction limit wave front propagation TEO - imaging 1:2 imaging using achromatic lenses Tilted object → tilted camera diffraction limited resolution < 10 µm for 2 mm field of view

  16. 0.5mm 10mm The wedged crystal (ZnTe) Change sensitivity vs. temporal resolution online

  17. Wedged crystal

  18. Simulation of EO-Response Function • incidence angle of laser • freq. dependent refraction • freq. dependent EO-coeff. • group velocity mismatch • multiple reflection First reflection of THz field e-beam Linear diode array 1000 pixel

  19. Simulation of EO-Response Function T=-50 fs origin 17% 100 pixel 5% more charge 20% shorter bunch

  20. 15 ns ns Challenge: detection at 1 MHz • ELIS photo-diode array (silicon video inc.): • Pixels: 1024 / 8 µm • Readout: 30 MHz • 1000 pixel -> 30 µs • 128 pixel -> 4 µs • Gating 15 ns • Low cost 

  21. Differences between TEO and SPPS • Pockels cell behind fs-oscillator ~ 100% of laser power available • all reflective shaper • 70 fs pulses (FWHM) at crystal are possible 60 nm transmission through the whole system • jitter: no regenerative laser amplifier - but larger distance to experiment • gating by detection (line camera) • wedge crystal – change temporal resolution continuously and online • More than 20 motors / 6 cameras – TEO can be entirely remote controlled

  22. EOS Timing monitor for the FEL-optical pump-probe Experiments • Flexible EOS system to test various concepts • scanning EO • chirped pulse EO • Electron bunch diagnostic • longitudinal bunch structure • Sub 15 fs Femtolaser • Located in container close to the accelerator • 15 m beamline (future upgrade: amplified pulse / single shot correlation) • Container electrically isolated / RF shielding • Temperature stabilized RF cable • Beamline for CTR -> EOS in container ( test of crystals …)

  23. EOS - Setup To spectrometer OTR TiSa fs pulse 65 nm FWHM / 15 fs electrons ZnTe crystal 300 µm

  24. Conclusion • 2 EOS systems • to test different EO schemes • Cross-check • (Goal) Measure at 1 MHz – each pulse • Machine diagnostics • Essential for user pump-probe experiments • TEO • 50 fs arrival time monitor • Highly automated (standard diagnostics) • EOS • 100 fs longitudinal electron bunch resolution

  25. Dies ist eine schöne vorlage ...

  26. TEO in numbers • shaper: • 640 element LCD matrix, 1800 l/mm grating , 500 mm focal distance • wavelength transmission: 800 +- 30 nm • TOD compensation = 1.2 107 fs3 • compressor: • 1500 l/mm gratings / 140 mm wide / 1.2m separation • wavelength transmission: 800 +- 30 nm • TOD induced = 1.4 107 fs3 • fiber: • 170 m long • Single mode polarization maintaining • TOD induced = 0.5 107 fs3 • cutoff wavelength < 780 nm

  27. Principal of electro-optical sampling • Sampling: • simple analysis • balanced detector allows high sensitivity • good synchronization required • multi-shot method • arbitrary time window possible PD Er • Chirp laser method: • single shot method • some more effort for laser and laser diagnostics required • resolution due to laser ~ √t0· tchirp • time window ~ 1-20ps Principal of temporal-wavelength correlation camera Er

  28. Space -time correlation method laser is „early“ laser is „late“ Er camera v v v Timing o.k. laser EO-Crystal

  29. the phase shaper - principle actual shaper

  30. 50% 50% Time structure and energy budget Ti:Sa oscillator pulses ~ 1600 ns 2.5 nJ Pockels cell 1 MHz 1 MHz X 1000 Pump-probe experiment 90% OPA ~ 800 ns 9.3 ns 0.01% 108 MHz 98% t = 0 ns 10% 10% SHG 90% 91% 92% Rotator 0.6% 50% 0.6% t = 1600 ns 0.6% 5% PM stretcher 15 pJ SHG SLM Feedback Fiber length PM fiber 92% ~ 800 ns Synchronized to electron beam at EO-crystal Synchronized to VUV-FEL beam at sample Pulse for SHG sampling the fiber length Pulse for SHG for reference 10% tunnel 50% 130 pJ e-bunch 2*40 pJ EO-crystal gated detector

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