VUV FEL HELMHOLTZ GEMEINSCHAFT EO systems at the
- Slides: 30
VUV FEL HELMHOLTZ GEMEINSCHAFT 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)
The 2 EOS systems VUV FEL HELMHOLTZ GEMEINSCHAFT Ti. Sa pump-probe fs-laser fs-oscillator for FEL-experiments EOS „Electro Optical Sampling“ chirped laser pulse TEO „Timing Electro Optical sampling“ 45° - geometry
Timing. EO VUV FEL HELMHOLTZ GEMEINSCHAFT 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 delay + jitter delay
Layout: pump-probe experiments VUV FEL HELMHOLTZ GEMEINSCHAFT FEL pulse Optical pulse to TEO optical laser
TEO VUV FEL HELMHOLTZ GEMEINSCHAFT Pockels cell 50 % beam splitter
The laser hutch VUV FEL HELMHOLTZ GEMEINSCHAFT TEO overview picture - CDR layout
The TEO layout - in the laser hutch VUV FEL HELMHOLTZ GEMEINSCHAFT laser hutch - CDR layout
The TEO layout - in the tunnel VUV FEL HELMHOLTZ GEMEINSCHAFT High degree of automation tunnel - CDR layout 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 -
TEO - first steps. . . VUV FEL HELMHOLTZ GEMEINSCHAFT Laser hutch Accelerator tunnel
TEO - simulations VUV FEL HELMHOLTZ GEMEINSCHAFT 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
HELMHOLTZ GEMEINSCHAFT introducing LAB II simulation software VUV FEL Simulation of fs-pulse propagation by Th. Feurer and group (Jena / MIT /Bern) ü time - frequency domain (no spatial calculations) ü linear and nonlinear effects / three wave mixing ü various materials ü compressors, strechers and phase shaper ü auto- / cross-correlation, FROGs ü and much more Based on Lab. View t a ad o l wn e o d. d e b 2 e a r l. F w ww
Lab II - simulation of TEO VUV FEL HELMHOLTZ GEMEINSCHAFT ~ 70 fs FWHM
The compressor VUV FEL HELMHOLTZ GEMEINSCHAFT 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 fs 3 / TOD by compressor: 1 -2 107 fs 3 optimization dilemma bandwidth transmission induced TOD (constant grating size) highly dispersive gratings (1800 lines / mm) low dispersive gratings (1200 lines / mm)
the phase shaper - actual design VUV FEL HELMHOLTZ GEMEINSCHAFT folding mirror 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)
TEO - imaging HELMHOLTZ GEMEINSCHAFT VUV FEL 1: 2 imaging using achromatic lenses Tilted object → tilted camera diffraction limited resolution < 10 µm for 2 mm field of view ray tracing well below diffraction limit wave front propagation
The wedged crystal (Zn. Te) VUV FEL HELMHOLTZ GEMEINSCHAFT Change sensitivity vs. temporal resolution online 0. 5 mm 10 mm Thick crystal Thin crystal Signal Temporal resolution
Wedged crystal HELMHOLTZ GEMEINSCHAFT VUV FEL
Simulation of EO-Response Function VUV FEL HELMHOLTZ GEMEINSCHAFT First reflection of THz field e-beam Linear diode array 1000 pixel • incidence angle of laser • freq. dependent refraction • freq. dependent EO-coeff. • group velocity mismatch • multiple reflection
Simulation of EO-Response Function VUV FEL HELMHOLTZ GEMEINSCHAFT origin T=-50 fs 17% 100 pixel 5% more charge 20% shorter bunch
Challenge: detection at 1 MHz VUV FEL HELMHOLTZ GEMEINSCHAFT ELIS photo-diode array (silicon video inc. ): Ø Pixels: 1024 / 8 µm Ø Readout: 30 MHz Ø 1000 pixel -> 30 µs Ø 128 pixel -> 4 µs 15 ns ØGating 15 ns ØLow cost ns
Differences between TEO and SPPS HELMHOLTZ GEMEINSCHAFT VUV FEL Ø Pockels cell behind fs-oscillator ~ 100% of laser power available Ø all reflective shaper Ø 70 fs pulses (FWHM) at crystal are possible 60 nm transmission through the whole system Ø jitter: no regenerative laser amplifier - but larger distance to experiment Ø gating by detection (line camera) Ø wedge crystal – change temporal resolution continuously and online ØMore than 20 motors / 6 cameras – TEO can be entirely remote controlled
EOS HELMHOLTZ GEMEINSCHAFT 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 üSub 15 fs Femtolaser üLocated in container close to the accelerator ü 15 m beamline (future upgrade: amplified pulse / single shot correlation) üContainer electrically isolated / RF shielding üTemperature stabilized RF cable üBeamline for CTR -> EOS in container ( test of crystals …) VUV FEL
EOS - Setup VUV FEL HELMHOLTZ GEMEINSCHAFT To spectrometer OTR Ti. Sa fs pulse 65 nm FWHM / 15 fs electrons Zn. Te crystal 300 µm
Conclusion HELMHOLTZ GEMEINSCHAFT • 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 VUV FEL
VUV FEL HELMHOLTZ GEMEINSCHAFT Dies ist eine schöne vorlage. . .
TEO in numbers HELMHOLTZ GEMEINSCHAFT shaper: • 640 element LCD matrix, 1800 l/mm grating , 500 mm focal distance • wavelength transmission: 800 +- 30 nm • TOD compensation = 1. 2 107 fs 3 compressor: • 1500 l/mm gratings / 140 mm wide / 1. 2 m separation • wavelength transmission: 800 +- 30 nm • TOD induced = 1. 4 107 fs 3 fiber: • 170 m long • Single mode polarization maintaining • TOD induced = 0. 5 107 fs 3 • cutoff wavelength < 780 nm VUV FEL
VUV FEL HELMHOLTZ GEMEINSCHAFT Sampling: • simple analysis • balanced detector allows high sensitivity • good synchronization required • multi-shot method • arbitrary time window possible Chirp laser method: • single shot method • some more effort for laser and laser diagnostics required • resolution due to laser ~ √t 0· tchirp • time window ~ 1 -20 ps Principal of electro-optical sampling PD Er camera Er Principal of temporalwavelength correlation
Space -time correlation method VUV FEL HELMHOLTZ GEMEINSCHAFT laser is „late“ Timing o. k. laser is „early“ laser EO-Crystal Er v camera v v
the phase shaper - principle VUV FEL HELMHOLTZ GEMEINSCHAFT actual shaper
Time structure and energy budget VUV FEL HELMHOLTZ GEMEINSCHAFT Ti: Sa oscillator pulses ~ 1600 ns 2. 5 n. J Pockels cell 1 MHz 90% ~ 800 ns 90% 50% 9. 3 ns 91% Rotator 0. 6% 15 p. J 0. 6% stretcher 50% 108 MHz 98% SLM Feedback Fiber length 50% 92% fiber ~ 800 ns 10% 130 p. J e-bunch 50% tunnel 2*40 p. J EO-crystal gated detector 92% t = 1600 ns SHG 5% 10% X 1000 Pump-probe experiment OPA t = 0 ns SHG 0. 01% 10% PM PM 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
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