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THE OPTICAL REPLICA SYNTHESIZER AT FLASH

THE OPTICAL REPLICA SYNTHESIZER AT FLASH. new diagnostic tool for electron bunches Peter Salén Stockholm University. electron bunch properties: longitudinal density profile. slice emittance. slice energy spread. electron bunch: moving at v ≈ c. ca. 20 m m long.

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THE OPTICAL REPLICA SYNTHESIZER AT FLASH

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  1. THE OPTICAL REPLICA SYNTHESIZER AT FLASH new diagnostic tool for electron bunches Peter Salén Stockholm University

  2. electron bunch properties: longitudinal density profile slice emittance slice energy spread electron bunch: moving at v ≈ c ca. 20 mm long ca. 100 mm wide FEL is very sensitive to the properties of the electron bunch need to control and measure these properties! hard to measure directly  measure an optical copy instead

  3. Polarizer Building 28g Camera Photo diode Power meter Laser diagnostics Seed laser (775 nm) Translation stage FLASH tunnel OS0 OS2 OS1 FROG OTR screen OTR screen Electron beam Vert. pol. undulator (modulator) Hor. pol. undulator (radiator) Chicane Chicane

  4. MAGNETIC STRUCTURES • Undulators: • electromagnets • 5 periods • 40 mm gap, 0.5 T max. • Chicanes: • 4 dipole magnets

  5. SEED LASER Home built Er Fiber oscillator: Rep freq=54 MHz phase locked to RF l=1550 nm Amplified and frequency doubled, 1 mW Commercial Ti:Sapph Amplifier: Works according to CPA 0.7 mJ/pulse at 775 nm, 0.2-3 ps

  6. LASER-ELECTRON SYNCHRONIZATION delay FLASH 5 Hz trigger Er:fiber oscillator stretcher Ti:Sapph amplifier compressor to tunnel ca.54 MHz pulse train Fourier Transform 24th harmonic FLASH RF 1.3 GHz ca. 1.3 GHz ca.19 ns piezo + delay diff. freq. mixing vector modulator Matlab program

  7. TEMPORAL OVERLAP SCAN Overlap => microbunching => enhancement of coherent OTR Longitudinal profile for electron pulse. Distorted by jitter of a few 100 fs.

  8. GRENOUILLE Based on FROG technique (autocorrelator + spectrometer) 2D phase retrieval algorithm => fully characterized pulse Electric field profile => electron bunch profile Single shot measurement

  9. RESULTS Short electron bunch, 400 fs laser pulse FROG trace - Electron bunch profile -- Phase of optical replica pulse 150 fs FWHM Energy of optical replica pulse ~5 mJ Parasitic run of ORS while maintaining SASE operation

  10. Further compression of electron bunch Unexpected FROG trace – not analyzable Probably CSR from chicane or undulators

  11. REMAINING ISSUES • Comparison with other method - check of accuracy • 8-bit camera depth • Tests to clarify origin of unexpected FROG trace at high compression • Need higher laser intensity • Rebuilding ORS for sFLASH

  12. 3D ELECTRON DENSITY DISTRIBUTION ORS-setup without radiator or GRENOUILLE Image coherent OTR on camera. Short (170 fs) laser pulse => 2D images of transverse slices of electron bunch as a function of longitudinal coordinate Horizontal (- -), vertical (-) position of spot 3D electron bunch profile for long bunches > ps Also by coherent imaging of OTR

  13. OTHER APPLICATIONS OF THE ORS -Phase of optical replica => energy chirp of electron bunch -3D electron density distribution -Slice energy spread -Slice emittance -’echo’ test experiments (G. Stupakov, SLAC-PUB-13445, Oct.2008) -ORFIR

  14. SUMMARY • Spatial and temporal overlap between laser- and electron pulse • - Generated optical replica pulses and analyzed with FROG technique, bunch profile extracted • Parasitic run of ORS while maintaining SASE operation • 3D electron bunch profile measured on ps time scales and many other applications.

  15. COLLABORATORS Stockholm University: Peter van der Meulen Mathias Hamberg Mats Larsson Uppsala University: Volker Ziemann Gergana Angelova-Hamberg DESY: Holger Schlarb Florian Löhl Hamburg University: Joern Boedewadt Axel Winter Shaukat Khan BESSY: Atoosa Meseck DESY: E. Saldin, E. Schneidmiller & M. Yurkov

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