UK FEL development package WP6: femtosecond synchronisation and stability   Dr Steven Jamison Accelerator Science and Technology Centre (ASTeC) STFC Daresbury National Laboratory Daresbury, U.K. S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Context Pump-probe science at LCLS - science obscured by timing jitter - can be recovered from time-sorting, but with limitations. LCLS: ~ 170fs rms jitter LCLS measurement of Bismuth phonon dynamics, with & without time sorting S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

WP6: femtosecond synchronisation and stability Task 6.1 Characterisation of laser oscillator, amplified laser, master and high power RF phase noise sources with CLARA test-bed.   Systematic measurements of relative phase or arrival time in laser and RF systems throughout the CLARA facility. Measurements will require development of suitable RF-laser and laser-laser cross-correlation diagnostics, while low power RF measurements will utilise precision RF phase noise test equipment. Beam-based measurements (Schottky scan; energy stability) will complement direct sub-system investigations. Mitigations and sub-systems stability improvements will be implemented as part of continuous improvement. Where key subsystem solutions or problems are identified, knowledge exchange relationships will be sought with key laser and/or RF commercial providers to prepare these key technologies for a future UKFEL . S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Results RF oscillator Phase jitter analysis of RF clocks S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Analysis RF oscillator Phase jitter analysis of RF clocks Clock performance is dependent on selected frequency bandwidth: Ralab (VELA/CLARA ‘custom’ MO, repaired February 2017): integrated Δτrms = 86 fs Far out (>1 kHz): +2 fs (best performance) Close in (<1 kHz): +84 fs (worst performance) Rohde and Schwartz SMA100A: integrated Δτrms = 27 fs Far out (>1 kHz): +19 fs (worst performance) Close in (<1 kHz): +7 fs (best performance) Agilent (temporary loan): integrated Δτrms = 24 fs Far out (>1 kHz): +16 fs Close in (<1 kHz): 8 fs Spurs in Rohde and Schwartz at ~60, 120 Hz – mains coupling which accounts for +5 fs From device, or measurement artefact (signal contamination)? What noise bandwidth is important? S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Results Laser oscillator Phase jitter analysis of ‘laser’ Strictly speaking: the 36th harmonic of a signal produced by filtering and amplifying the voltage output produced by a fast photodiode generated by incident laser pulses from the optical cavity at a fundamental repetition rate of ~83.292 MHz Phase jitter analysis of ‘laser’ Spurs at 60/120 Hz from device – these are transferred to laser through PLL, not present in free-running mode S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Analysis Laser oscillator Phase jitter analysis of laser Laser-RF PLL has finite bandwidth, close in only: 10 Hz – 1 kHz PLL attempts to follow clock input over this range, so influenced by clock noise – note correlation of spurious Far-out contribution is limited by laser free running noise Locked/unlocked are very similar outside of PLL bandwidth S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Laser-RF synchronization Results Laser-RF synchronization Data so far has been ‘absolute’ noise – really the relative noise of the device with respect to the internal oscillator of the analyser. Statistics prevent us using absolute noise data to be make quantitative predictions about the relative noise between two devices, despite the common reference… Laser-RF relative noise Effect of PLL (direct) RF better than laser Laser better than RF The phase noise analyser has an option to pass the internal oscillator (like SMA?) as an output; by locking the laser to this we can do a relative noise measurement of the Femtolock at 2998.5 MHz. S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Laser-RF synchronization Analysis Laser-RF synchronization Laser-RF relative noise Integrated relative noise (synchronization) between laser and RF clock input (10 Hz – 1 MHz) – ΔτRMS = 13 fs Manufacturer quotes 7 fs for integrated 3 kHz – 10 MHz; c.f. 8 fs for 3 kHz to 1 MHz measured in-house Good agreement but also dependent on oscillator choice (manufacturer did not provide that information) Based on absolute noise spectra and relative measurement, can make reasonable judgement as to factors limiting relative noise: 10 Hz – 1 kHz; 2.4 fs – direct effect of PLL (laser cavity doesn’t quite follow source) 1 kHz – 10 kHz; 4.8 fs – RF oscillator is better than free-running laser 10 kHz+ - 5.8 fs – free-running laser noise is better than RF oscillator S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Results Clock distribution Relative phase jitter analysis of Libera Sync clock distribution Integrated (10 Hz – 1 MHz): Δτrms = 8.2 fs Close in (<1 kHz): 1.1 fs Far out (> 1 kHz): 7.1 fs S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Analysis Clock distribution Additive phase jitter analysis of Libera Sync clock distribution Note: relative measurement of distribution performed: compares RF clock before and after distribution Performance is dependent on selected frequency bandwidth: Far out: +7.1 fs – but not real? Comment from manufacturer i-tech: “There is a bump in the MHz range that is not real and is present because of two reasons: 1) there is a narrow filter in the receiver unit that cuts the noise in the MHz range and when comparing the source with the one coming out it seems like the Libera is adding noise…” “There is another contribution to the bump because of the integrated optics. The optical signal is travelling through 800 m of optical fiber (spool in the transmitter unit) and at the end we have a kind of phase dispersion in the noise. The difference [between the input and output] can be observed as a bump” “If a very clean RF source is used the contribution can be reduced. Stephan Hunziker did such measurements at PSI and obtained 3.8 fs integrated (10 Hz – 10 MHz) Far out then may be as low as 2.7 fs… This is a state-of-the-art device S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

WP6: femtosecond synchronisation and stability Task 6.2 400Hz stability   Determine the sub-system causes of shot-shot instabilities in the electron beam properties, using CLARA as test-bed (e.g. electrical mains phase dependence RF phase and amplitude); develop feedforward solutions enabling stable mains-asynchronise pulsing. S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

WP6: femtosecond synchronisation and stability Task 6.3 Optical master oscillator   Develop and demonstrate an RF master oscillator derived directly from the photocathode laser oscillator; evaluate stability performance, confirm (or otherwise) improvements over existing RF and optical master oscillators. S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Analysis Laser oscillator Laser as RF clock? Integrated jitter (10 Hz – 10 MHz) of RF extracted from locked laser is comparable to RF oscillator: Laser (+ photodiode, low noise amplifier): ΔτRMS = 29 fs Rohde & Schwartz SMA100: ΔτRMS = 27 fs Why is locked laser a good clock? Forming hybrid with best of both: Good close in performance of RF oscillator Good far out performance of laser Emphasises importance of relationship between PLL bandwidth and free running noise; for low integrated phase noise Reference should have low phase noise in PLL range Locked client should have low free-running phase noise outside PLL range S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Optical RF oscillator – CLARA development & testing RF distribution LLRF Linacs S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Optical RF oscillator – CLARA development & testing First working system in hand ….optimisation started RF distribution LLRF Linacs S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

WP6: femtosecond synchronisation and stability Task 6.4 sub-5 femtosecond electron beam and photon beam arrival diagnostics   Develop electron, photon and RF arrival-time/phase diagnostics for the above programme, and for use in UKFEL stabilisation and time-stamping systems. S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

WP6: femtosecond synchronisation and stability Task 6.5 Start-end timing stability evaluations for ‘model’ UKFEL Examine accelerator and FEL design with stability optimisation. S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017

Slide title S.P. Jamison , UK FEL meeting, STFC Daresbury Laboratory, July 2017