Installation Progress of the Laser-based Synchronization System at FLASH.

Transcription

1 Installation Progress of the Laser-based Synchronization System at FLASH. Overview, Experiences, Performance and Outlook Sebastian Schulz 1,2 on behalf of the FLASH LbSyn Team 1 Institute of Experimental Physics Hamburg University, Germany 2 Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany 48th ICFA Advanced Beam Dynamics Workshop on Future Light Sources March 1 5, 2010 S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

2 Outline. 1 Introduction and Overview 2 Progress and Results of Selected Subsystems Master Laser Oscillator Fiber Links Laser-to-Laser Synchronization Infrastructure and Electronics 3 Latest Development Photoinjector Laser Synchronization 4 Summary and Outlook S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

3 Introduction and Overview Optical Synchronization Systems. Overview projected point-to-point stability: 10 fs enable the implementation of a longitudinal feedback system S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

4 Introduction and Overview The Laser-based Synchronization System at FLASH. Layout, Implementation and Upgrades RF gun BAM EBPM BAM BCM EBPM BAM BCM ACC1 ACC39 ACC2 ACC3 ACC4 ACC5 ACC6 ACC7 RF RF RF RF RF injector laser 1 master laser FL FL oscillator EDFL FL FL OXC RL RL FL 16-port FSD unit EDFAs FL FL FL FL add. diag RF FL FL FL master laser oscillator SESAM OXC OXC EO/THz seed laser laser OXC Yb ber laser bypass OXC pump-probe laser EO seeding undulators BAM SASE undulators photon beam HHG EO/THz BAM dump target last user run (till September 2009) MLO with distribution and 4 fiber links, 3 BAMs, 1 EBPM (3 front-ends), standard BCMs, EO with Ti:sapphire laser S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

5 Introduction and Overview The Laser-based Synchronization System at FLASH. Layout, Implementation and Upgrades RF gun (exchanged) BAM EBPM BAM BCM EO EBPM BAM BCM ACC1 ACC39 EO ACC2 ACC3 ACC4 ACC5 ACC6 ACC7 RF RF RF RF RF injector laser 2 OXC master laser FL FL oscillator EDFL FL FL RL FL 16-port FSD unit RL FL EDFAs FL FL Yb FL Orange FL add. diag RF FL FL FL master laser oscillator SESAM OXC RF OXC EO/THz seed laser laser OXC Yb ber laser bypass OXC RF pump-probe laser EO seeding undulators BAM SASE undulators photon beam HHG EO/THz BAM dump target last user run (till September 2009) MLO with distribution and 4 fiber links, 3 BAMs, 1 EBPM (3 front-ends), standard BCMs, EO with Ti:sapphire laser after the FLASH upgrade (just finished, now in commissioning phase)... S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

6 Introduction and Overview The Laser-based Synchronization System at FLASH. Layout, Implementation and Upgrades RF gun (exchanged) BAM EBPM BAM BCM EO EBPM BAM BCM ACC1 ACC39 EO ACC2 ACC3 ACC4 ACC5 ACC6 ACC7 RF RF RF RF RF injector laser 2 OXC master laser FL FL oscillator EDFL FL FL RL FL 16-port FSD unit RL FL EDFAs FL FL Yb FL Orange FL add. diag RF FL FL FL master laser oscillator SESAM OXC RF OXC EO/THz seed laser laser OXC Yb ber laser bypass OXC RF pump-probe laser EO seeding undulators BAM SASE undulators photon beam HHG EO/THz BAM dump target last user run (till September 2009) MLO with distribution and 4 fiber links, 3 BAMs, 1 EBPM (3 front-ends), standard BCMs, EO with Ti:sapphire laser upgraded MLO and distribution, 3 more fiber links, 1 new BAM, 1 new EBPM, new BCM setups, new EO station, new OXC-I, improved infrastructure, and more S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

7 Progress and Results of Selected Subsystems Master Laser Oscillator Master Laser Oscillator I. Overview and Current Status Specifications/Requirements photo diode topology: EDFL in σ-configuration Er-doped fiber OSA, amplitude mon. repetition rate: MHz collimator average power: 100 mw WDM L/4 L/2 PBC autocorrelator pulse duration < 100 fs (rms) isolator L/2 to free-space integrated timing jitter < 15 fs in the interval [1 khz, 10 MHz] pump combiner coll. L/4 L/2 PBC L/4 L/2 PBC distribution mechanically robust, easy to maintain piezo mirror on motorized stage established additional diagnostics to ensure single-pulse operation 980 nm pump diodes S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

8 Progress and Results of Selected Subsystems Master Laser Oscillator Master Laser Oscillator I. Overview and Current Status Specifications/Requirements topology: EDFL in σ-configuration repetition rate: MHz average power: 100 mw pulse duration < 100 fs (rms) integrated timing jitter < 15 fs in the interval [1 khz, 10 MHz] mechanically robust, easy to maintain established additional diagnostics to ensure single-pulse operation back to breadboard design (severe issues with engineered versions) prepared for further automatization, exception handling in operation for > 6 months without major problems S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

9 Progress and Results of Selected Subsystems Master Laser Oscillator Master Laser Oscillator II. Some Recent Results SSB phase noise L! (dbc/hz) free running, P = 10.8 mw > u2t photo monitor port, Vbias = 7.00 V, thick RF cable RF@2.6 GHz = 10.4 dbm, att. = 10 db, 1000 corr., no avg., open housing integr. timing jitter = 11.5 fs integrated timing jitter (fs) integrated timing jitter 11.5 fs in the interval [1 khz, 10 MHz] offset frequency (Hz) S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

10 Progress and Results of Selected Subsystems Master Laser Oscillator Master Laser Oscillator II. Some Recent Results MLO2 relative optical power peak to peak = , standard deviation = integrated timing jitter 11.5 fs in the interval [1 khz, 10 MHz] amplitude drift over 240 h: < 2% (peak-to-peak), 0.4% (rms) no active stabilization time (h) S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

11 Progress and Results of Selected Subsystems Master Laser Oscillator Master Laser Oscillator II. Some Recent Results auto correlation signal (a.u.) measured data taup = 87.3 fs delay (fs) integrated timing jitter 11.5 fs in the interval [1 khz, 10 MHz] amplitude drift over 240 h: < 2% (peak-to-peak), 0.4% (rms) no active stabilization pulse duration τ p = 87 fs, from sech 2 (t/τ p )-fit important for fiber link dispersion compensation S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

12 Progress and Results of Selected Subsystems Master Laser Oscillator Master Laser Oscillator III. Alternative Concept: Investigation of a Commercial Laser System Promising: OneFive ORIGAMI-15 topology: unknown (SESAM, soliton) repetition rate: MHz average power: > 100 mw pulse duration: τ p < 150 fs integrated timing jitter < 5 fs in the interval [1 khz, 10 MHz] mechanically robust, easy to maintain (sealed housing, one button) ordered custom system delivery/installation: April 2010 PSI enabled progress on direct conversion November open questions: long-term stability, life-time Timing Jitter [fs] Origami / Direct Conversion RF Phase Noise: 4.3 fs V, 13 mv, 1.5 GHz, 4.2 dbm k 10k 100k 1M 10M Frequency [Hz] integrated timing jitter: 4.3 fs SSB PhaseNoise [dbc/hz] S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

13 Progress and Results of Selected Subsystems Fiber Links Actively Length-Stabilized Fiber Links I. Experiences with the Engineered Version Design: 3 Layers free-space optics S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

14 Progress and Results of Selected Subsystems Fiber Links Actively Length-Stabilized Fiber Links I. Experiences with the Engineered Version Design: 3 Layers free-space optics fiber installations S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

15 Progress and Results of Selected Subsystems Fiber Links Actively Length-Stabilized Fiber Links I. Experiences with the Engineered Version Design: 3 Layers free-space optics fiber installations electronics compartment S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

16 Progress and Results of Selected Subsystems Fiber Links Actively Length-Stabilized Fiber Links I. Experiences with the Engineered Version Design: 3 Layers free-space optics fiber installations electronics compartment Problems motorized delay stage telescope design incoupling efficiency optical isolation of EDFA 20 minor issues solved, taken into account for in first redesign (manufacturing now) S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

17 Progress and Results of Selected Subsystems Fiber Links Actively Length-Stabilized Fiber Links I. Experiences with the Engineered Version Design: 3 Layers free-space optics fiber installations electronics compartment Problems motorized delay stage telescope design incoupling efficiency optical isolation of EDFA 20 minor issues solved, taken into account for in first redesign (manufacturing now) easy: dispersion compensated EDFA (between FSD and link box) advantageous: new pre-spliced DCF (lower insertion loss) major redesign considerations in progress end-of-year S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

18 Progress and Results of Selected Subsystems Fiber Links Actively Length-Stabilized Fiber Links II. Performance Example: Long-Term Drift fiber link in loop timing jitter (fs) LINK09 in loop timing jitter, mean = 0.91 fs, std = 0.08 fs LINK minute moving average LINK15 in loop, mean1 = 2.68 fs, std1 = 0.83 fs, mean2 = 1.11 fs, std2 = 0.28 fs LINK minute moving average time (h) engineered fiber link boxes ensure reliable operation LINK09 BAM UBC2 165 m FRM link-end returning pulses τ p = 115 fs LINK15 OXC EO 440 m loop-mirror link-end returning pulses τ p = 200 fs timing distribution to the femtosecond level over long periods out-of-loop measurement setup currently under consideration S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

19 Progress and Results of Selected Subsystems Laser-to-Laser Synchronization Laser-to-Laser Synchronization I. Idea and First Implementation RF Synchronization based on a RF down-mixing scheme timing jitter 35 fs S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

20 Progress and Results of Selected Subsystems Laser-to-Laser Synchronization Laser-to-Laser Synchronization I. Idea and First Implementation RF Synchronization based on a RF down-mixing scheme timing jitter 35 fs Optical Synchronization basis: non-linear optics more precise measurements timing jitter 10 fs issues: two individual oscillators different repetition rates different wavelengths S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

21 Progress and Results of Selected Subsystems Laser-to-Laser Synchronization Laser-to-Laser Synchronization I. Idea and First Implementation RF Synchronization based on a RF down-mixing scheme timing jitter 35 fs Optical Synchronization basis: non-linear optics more precise measurements timing jitter 10 fs issues: two individual oscillators different repetition rates different wavelengths Characterization & Drift Measurements only possible with out-of-loop measurement requires second OXC S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

22 Progress and Results of Selected Subsystems Laser-to-Laser Synchronization Laser-to-Laser Synchronization I. Idea and First Implementation RF Synchronization based on a RF down-mixing scheme timing jitter 35 fs Optical Synchronization basis: non-linear optics more precise measurements timing jitter 10 fs issues: two individual oscillators different repetition rates different wavelengths Characterization & Drift Measurements only possible with out-of-loop measurement requires second OXC S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

23 Progress and Results of Selected Subsystems Laser-to-Laser Synchronization Laser-to-Laser Synchronization II. Single-Crystal Two-Color Balanced Optical Cross-Correlator 2 BBO GDD 1 HR@527.7nm HT@ 800&1550nm HT@ 527.7nm HR@ 800&1550nm sum frequency generation (SFG) in type-i ( ) phase-matched BBO crystal group delay, then again SFG measurement of SFG intensities difference signal highly sensitive to timing changes (nearly) independent on amplitude noise of the lasers ( balanced ) input signal for PLL S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

24 Progress and Results of Selected Subsystems Laser-to-Laser Synchronization Laser-to-Laser Synchronization III. Performance of the Optical Lock of the EO experiment s Ti:Sapphire Laser Gaussian fit raw data fit slope = 29.5 mv/fs OXC2 difference signal (V) relative timing change (fs) relative time delay t (fs) RF lock, jitter = 19.3 fs (rms over 400 s) 60 optical lock, jitter = 7.9 fs (rms over 400 s) time (s) used to lock, i.e. first cross-correlator measured by scanning an optical delay stage out-of-loop signal challenging task to reproduce routinely/automatically timing jitter over 400 s: 7.9 fs (rms), practically no drift RF lock over 400 s: 19.3 fs (rms) S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

25 Progress and Results of Selected Subsystems Infrastructure and Electronics Infrastructure and Electronics. Some Important and Critical Points Infrastructure new climatization in the synchronization hutch new power supplies with battery backup for optical table and critical rack-chassis new power supplies for BAM/EBPM installations in the tunnel improved BCM, VME & cabling installations in the tunnel S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

26 Progress and Results of Selected Subsystems Infrastructure and Electronics Infrastructure and Electronics. Some Important and Critical Points Infrastructure new climatization in the synchronization hutch new power supplies with battery backup for optical table and critical rack-chassis new power supplies for BAM/EBPM installations in the tunnel improved BCM, VME & cabling installations in the tunnel Electronics & Software addressed all issues of the fast ADC for BAM and EBPM readout improved VME laser diode drivers extension of the RF-lock server (exception handling!) polarization/amplitude feedback for the fiber links better failure detection and remote control S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

27 Progress and Results of Selected Subsystems Infrastructure and Electronics Infrastructure and Electronics. Some Important and Critical Points Infrastructure new climatization in the synchronization hutch new power supplies with battery backup for optical table and critical rack-chassis new power supplies for BAM/EBPM installations in the tunnel improved BCM, VME & cabling installations in the tunnel Electronics & Software addressed all issues of the fast ADC for BAM and EBPM readout improved VME laser diode drivers extension of the RF-lock server (exception handling!) polarization/amplitude feedback for the fiber links better failure detection and remote control important for a robust and reliable system time-consuming and expensive S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

28 Latest Development Photoinjector Laser Synchronization Photoinjector Laser Synchronization I. Motivation New BAM upstream of First Chicane timing change: δt beam = G gun δt gun + G laser δt laser with δt gun = δφgun ω RF and δt laser = δφ laser ω RF variation of gun and laser phase: δt gun + δt laser = 2.12 ps/deg (32% + 68%) variation of RF-gun phase slope: δt max = 0.52 ps RF-gun phase feed-forward or feedback requires arrival-time information of photoinjector laser pulses on cathode! optical cross-correlator Variation of arrival time [ps] Averaged arrival time of bunches [ps] Laser dt/d! = ps/deg Gun dt/d! = ps/deg Change of Gun or Laser phase [deg] 3.6 deg/ms 4.2 deg/ms 4.8 deg/ms 5.4 deg/ms 6.0 deg/ms Bunch number in macro pulse (10µs bunch spacing) [No #] S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

29 Latest Development Photoinjector Laser Synchronization Photoinjector Laser Synchronization II. Prototype Implementation at FLASH BBO LBO flashlamps diode amplifier & pulse picker photoinjector laser 2 Nd:YLF osc. EOM AOM AOM RF gun toroid e dispersion comp. EDFA L4, delay line Optical X-Correlator 1047 nm ~ 15 nj 27 MHz manual shifter 1.3 GHz 108 MHz 13.5 MHz MO MDR ADC ADC ADC controller DAC DAC Q I LDD controller MDR VME + Beckhoff or utca system ADC ADC ADC LO generation 20m SMF, PSOF, or RF-based FiberLink f R MLO synch. hutch MLO delivers precise timing information over an optical fiber measuring timing jitter between PTO and reference on O(10 fs) level with the optical cross-correlator stabilize 1.3 GHz phase of the PTO s EOM by a feed-forward algorithm or a control loop S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

30 Latest Development Photoinjector Laser Synchronization Photoinjector Laser Synchronization III. Single-Crystal Two-Color Balanced Optical Cross-Correlator "2" fast detectors "1" input 1550 nm 216 MHz 200 fs FWHM 628 nm BBO crystal L = 5 mm HR@628nm HT@1047&1550nm HR@1047nm HT@1550nm fixed end mirror input 1047 nm 27 MHz (10 Hz burst) 12 ps FWHM adjustable end mirror one short pulse (126 fs) and one long pulse ( 4 ps) sum frequency generation (SFG) in type-i ( ) phase-matched BBO crystal separation of pulses, delay with mirror, then again SFG measure sum frequency intensity shot-by-shot with fast detectors and ADCs (ν rep = 27 MHz) S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

31 Latest Development Photoinjector Laser Synchronization Photoinjector Laser Synchronization III. Single-Crystal Two-Color Balanced Optical Cross-Correlator S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

32 Latest Development Photoinjector Laser Synchronization SFG forward SFG backward Photoinjector Laser Synchronization IV. First Results 11.5 ps FWHM auto correlation signal (a.u.) normalized intensity (a.u.) time delay (ps) PRELIMINARY scan delay between MLO and PTO pulse SFG in both directions of OXC measure for PTO pulse duration 4.9 ps (rms) delay with mirror for second SFG not adjusted correctly S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

33 Summary and Outlook Summary and Outlook. Current Status of Upgrades to the Optical Synchronization System 1 many new components and subsystems 2 considerable progress towards a robust, reliable and engineered system 3 implementation of a longitudinal feedback S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

34 Acknowledgements Acknowledgements. Thank you for your attention! The FLASH LbSyn Team M. K. Bock, M. Felber, P. Gessler, K. E. Hacker, F. Ludwig, H. Schlarb, B. Schmidt, S. Schulz, L. G. Wissmann and its former members V. Arsov, F. Loehl, A. Winter, J. Zemella with its many collaborators, technicians and people of other groups S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

35 Additional Slides: RF, L-Testsetup, FiberLink Principle... RF-Lock Electronics for Ti:Sapphire Lasers RF-Lock Electronics for Ti:Sapphire Lasers. Extended RF Circuit with 81 MHz, 1.3 GHz and 9.1 GHz Phase-Detectors S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

36 Additional Slides: RF, L-Testsetup, FiberLink Principle... Laser-to-Laser Synchronization Laser-to-Laser Synchronization A-I. Idea and First Implementation test reference laser EDFL (self-built) λ 1 = 1550 nm, λ 1 = 100 nm τ FWHM,1 = 120 fs f rep,1 = MHz experiment s laser Ti:Sapphire oscillator (Coherent Micra-5) λ 1 = 800 nm, λ 1 = 65 nm τ FWHM,1 = 35 fs f rep,2 = MHz RF Synchronization based on a RF down-mixing scheme timing jitter 35 fs Optical Synchronization basis: non-linear optics more precise measurements timing jitter 10 fs issues: two individual oscillators different repetition rates different wavelengths Characterization & Drift Measurements only possible with out-of-loop measurement requires second OXC S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

37 Additional Slides: RF, L-Testsetup, FiberLink Principle... Laser-to-Laser Synchronization Laser-to-Laser Synchronization A-II. Implementation using the FLASH EO Ti:Sapphire Laser System Layout S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

38 Additional Slides: RF, L-Testsetup, FiberLink Principle... Fiber Links Actively Length-Stabilized Fiber Links A-I. Principle of Operation S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

39 Additional Slides: RF, L-Testsetup, FiberLink Principle... Fiber Links Actively Length-Stabilized Fiber Links A-I. Principle of Operation sum frequency generation (SFG) of reference and reflected pulses in type-ii phase-matched PPKTP crystal, delay, then again SFG measurement of SFG intensities difference signal highly sensitive to timing changes (nearly) independent on amplitude noise of the lasers ( balanced ) input signal for PLL (acting on piezo stretcher and delay stage) S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

40 Additional Slides: RF, L-Testsetup, FiberLink Principle... Free-Space Distribution Free-Space Distribution A-I. Schematics and Implementation designed for redundant two laser operation allows for setting optical power per device no dispersive pulse broadening S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

41 Additional Slides: RF, L-Testsetup, FiberLink Principle... Free-Space Distribution Free-Space Distribution A-I. Schematics and Implementation designed for redundant two laser operation allows for setting optical power per device no dispersive pulse broadening S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

42 Additional Slides: RF, L-Testsetup, FiberLink Principle... Free-Space Distribution Free-Space Distribution A-II. Measurements transmission T p, reflection R s (%) Transmission and Reflection of Newport 05FC16BC.9 at 1550 nm specification: T p > 90 %, R s > 99.5% (w/o surfaces) Tp meas. 1, rms deviation = 0.96 % Tp mean 1 = % Tp meas. 2, rms deviation = 1.08 % Tp mean 2 = % Rs meas. 1, rms deviation = 0.39 % Rs mean 1 = % Rs meas. 2, rms deviation = 0.66 % Rs mean 2 = % beam cube number beam cubes do not meet specs (to a small amount) use only the best ( QA) Optical Power Drift 0.3% (peak-to-peak) over 14 h but: cannot distinguish between temperature and pointing stability S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25

43 Additional Slides: RF, L-Testsetup, FiberLink Principle... Free-Space Distribution Free-Space Distribution A-II. Measurements Transmission and Reflection of Newport 05FC16BC.9 at 1550 nm Optical Power Drift transmission T p, reflection R s (%) specification: T p > 90 %, R s > 99.5% (w/o surfaces) Tp meas. 1, rms deviation = 0.96 % Tp mean 1 = % Tp meas. 2, rms deviation = 1.08 % Tp mean 2 = % Rs meas. 1, rms deviation = 0.39 % Rs mean 1 = % Rs meas. 2, rms deviation = 0.66 % Rs mean 2 = % beam cube number beam cubes do not meet specs (to a small amount) use only the best ( QA) consider also alternative schemes: dispersion compensated high-power EDFA hybrid design: free-space + fiber splitter(s) 0.3% (peak-to-peak) over 14 h but: cannot distinguish between temperature and pointing stability can it be done better? S. Schulz (Hamburg U, DESY) FLASH Optical Synchronization FLS Workshop / 25