John Corlett, July 2004 Overview of laser, timing, and synchronization issues John Corlett, Larry Doolittle, Bill Fawley, Steven Lidia, Bob Schoenlein, John Staples, Russell Wilcox, Sasha Zholents LBNL

John Corlett, July 2004 Diffraction and spectroscopy Nuclear positions and electronic, chemical or structural probes Scientific goal - application of ultrafast x-ray sources to study dynamics with high-resolution diffraction angle time delay x-ray probe visible pump detector Time-resolved x-ray diffraction Time-resolved EXAFS NEXAFS delay x-ray probe visible pump r energy time K edge absorption f(r) Plus photoelectron spectroscopy, photoemission microscopy, etc Access new science in the time-domain x-ray regime

John Corlett, July 2004 Ultrafast laser pulse “pumps” a process in the sample Ultrafast x-ray pulse “probes” the sample after time ∆t Ultrafast lasers an integral part of the process X-rays produced by radiation in an electron accelerator Pump-probe experiment concept Laser excitation pulse X-ray probe pulse ∆t ion or e - detector  -detector sample

John Corlett, July 2004 Both laser and x-ray pulses should be stable in temporal and spatial distributions Parameters and quality of x-ray pulse determined by the electron beam Accelerator parameters Synchronization between laser and x-ray pulses, ∆t, should ideally be known and controllable - to the level of the pulse duration itself ~ 10 fs Pump-probe experiment concept Laser excitation pulse X-ray probe pulse ∆t ion or e - detector  -detector sample

John Corlett, July 2004 Many projects around the world are addressing the need for ultrafast x-rays, in different ways LCLS: linac SASE (construction) BNL DUV FEL: linac HGHG (operational) DESY TTF-II: linac SASE (construction) SPPS: linac spontaneous emission from short bunches (operational) ALFF: linac SASE BESSY FEL: linac HGHG European X-ray FEL: linac SASE Daresbury 4GLS: ERL HGHG + spontaneous LUX: recirculating linac HGHG + spontaneous Cornell ERL: ERL spontaneous MIT-Bates X-ray FEL: linac HGHG + SASE Arc-en-Ciel: recirculating linac / ERL HGHG + SASE linac HGHG BNL PERL: ERL spontaneous

John Corlett, July 2004 What are the difficulties in achieving x-ray beam quality? X-rays are produced by electrons emitting synchrotron radiation in an accelerator The electron beams are manipulated by rf and magnetic systems The x-ray beam quality is limited by the electron beam quality in many ways –Electron bunch charge, energy, emittance, energy spread, bunch length, position, … At the radiator! Production of high-brightness bunches is tough enough –Emission process, space charge, rf focusing, …. Then we must accelerate and otherwise manipulate the bunches before they reach the radiating insertion device Many opportunities to degrade the electron bunch –Space charge, rf focussing, emittance compensation, CSR, geometric wakefields, rf field curvature, resistive wall wakefields, optics aberrations, optics errors, alignment, rf phase errors, rf amplitude errors, …

John Corlett, July 2004 Synchronization In addition to the electron bunch properties, the need for synchronization of the x-ray pulse to a reference signal - the pump - is required for many experiments –Time between pump signal and probe x-ray pulse Predictable or measurable Stable to ~ pump & probe pulse durations This presents additional demands on the accelerator, instrumentation, and diagnostics systems Various techniques may be employed to enhance synchronization –Slit spoiler for SASE –Seeding HGHG ESASE (Enhanced SASE) –e - bunch manipulation & x-ray compression –Measurement of relative x-ray - pump laser timing Electro-optic sampling of electron bunch fields Time-resolved detection of x-ray and laser pulses at the sample

John Corlett, July 2004 The roles of lasers, timing,and synchronization in an ultrafast x-ray facility Laser systems –Generate the high-brightness electron beam in an rf photocathode gun –Produce the pump signals at the beamline endstations Timing system –Provides reference signals to trigger (pulsed) accelerator systems –Provides reference waveforms to synchronize rf systems –Provides reference waveforms to synchronize endstation lasers Synchronization –To control and determine the timing of the x-ray pulse with respect to a pump pulse –Requires stable systems in the x-ray facility, connected by a “stable” timing system including stable timing distribution systems The timing system only has to be “stable” enough for all of the components connected to it to follow it’s timing jitter (to the required level) Phase noise  timing jitter The majority of the timing jitter must be within the bandwidth of the accelerator & laser systems such that they can follow –Local feedback around rf & laser systems –Lock to timing system master oscillator

John Corlett, July 2004 Phase noise and timing jitter

John Corlett, July 2004 Some space and time parameters for a conceptual ultrafast x-ray facility rf photocathode gunLinac Undulators Bend magnets / compressor End stations 10 fs ≈ 3 µm at c Thermal expansion for ∆T = 0.1°C in Cu over 100 m ≈ 170 µm or 570 fs Similar magnitude effect from refractive index change in optical fiber Length scale ~ 100’s m Time scale ~ µs Equivalent bandwidth ~ 100’s kHz

John Corlett, July 2004 Some rf systems parameters for a conceptual ultrafast x-ray facility rf photocathode gunLinac Undulators Bend magnets / compressor End stations 10 fs ≈ 5x10 -3 °rf phase L-band Cavity filling time (Q=10 4 ) ≈ 2 µs Bandwidth ~ 100 kHz Cavity filling time (Q=10 7 ) ≈ 2 ms Bandwidth ~ 100 Hz 10 fs ≈ 1x10 -2 °rf phase S-band Cavity filling time (Q=10 4 ) ≈ 1 µs Bandwidth ~ 300 kHz

John Corlett, July 2004 Synchronize rf systems to a master oscillator Control phase and amplitude of the rf fields experienced by the electron beam The master oscillator must have a phase noise spectrum such that the majority of the timing jitter is accumulated within the bandwidth of the rf systems Local feedback ensures that the rf systems follow jitter in the master oscillator Noise sources Microphonics Thermal drift Electronic noise Digital word length

John Corlett, July 2004 Choice of master oscillator rf crystal oscillator has low noise close to carrier Laser has low noise above ~ 1 kHz Mode locked laser locked to good crystal oscillator provides a suitable master oscillator Active mode-lock cannot respond rapidly to perturbations

John Corlett, July 2004 Although there are very good low-noise sapphire loaded cavity oscillators

John Corlett, July 2004 Phase noise spectrum requirement Master oscillator phase noise within bandwidth of feedback systems can be corrected Residual uncontrolled phase noise plus noise outside feedback systems bandwidth results in timing jitter and synchronization limit

John Corlett, July 2004 Laser synchronization two independent psec Mira 900-P (Coherent) lasers PLLs at 80 MHz (n=1) and 14 GHz (n=175) D.J. Jones et al., Rev. Sci. Instruments, 73, 2843 (2002). time (sec) Sub-femtosecond timing jitter has been demonstrated between two mode- locked Ti:sapphire lasers Limit is electronic noise (under favorable conditions)

John Corlett, July 2004 Sophisticated laser systems are an integral component of an FEL facility Multiple beamline endstation lasers Photocathode laser FEL seed lasers Laser oscillator Spatial profiling Amplitude control Amplifier Pulse shaping Multiply Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning

John Corlett, July 2004 Lasers may be synchronized to a common master oscillator Photocathode laser FEL seed lasers Laser oscillator Spatial profiling Amplitude control Amplifier Pulse shaping Multiply Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Multiple beamline endstation lasers Laser master oscillator

John Corlett, July 2004 rf systems need to be synchronized to a common master oscillator Photocathode laser FEL seed lasers Laser oscillator Spatial profiling Amplitude control Amplifier Pulse shaping Multiply Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Multiple beamline endstation lasers Laser master oscillator ~

John Corlett, July 2004 rf signals for the accelerator may also be derived from the laser master oscillator Photocathode laser FEL seed lasers Accelerator RF signals Laser oscillator Spatial profiling Amplitude control Amplifier Pulse shaping Multiply Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Laser oscillatorAmplifier & conditioning Multiple beamline endstation lasers ~ ~ ~ ~~ ~ ~ Laser master oscillator

John Corlett, July 2004 rf photocathode gun

John Corlett, July 2004 rf photocathode laser Vertical lineout Horizontal lineout Time (ps) UV Power (V) File: cc120605, RMS length = 1.07 ps UV pulse time profile UV pulse on cathode W. S. Graves, MIT-Bates (DUV FEL, Brookhaven)

John Corlett, July 2004 rf photocathode laser W. S. Graves, MIT-Bates (DUV FEL, Brookhaven) HeadTail Time (ps) Current (A) File: phiminusg, FWHM = ps Time (ps) UV Power (V) File: cc120605, RMS length = 1.07 ps UV pulse time profile Bunch production, acceleration, and compression UV pulse on cathode –Non-uniformity exacerbates space-charge effects –Temporal non-uniformity induces micro-bunching

John Corlett, July 2004 Laser pulse shaping influences the emitted electron bunch grating stretcher Ti:sapphire Regenerative Amplifier Q-switched Nd:YAG (2  ) grating compressor Pulse Shaper Ti:sapphire Oscillator 100 fs, 2 nJ <0.5 ps jitter RF from master oscillator 2  3  >1 mJ, 800 nm, 10 kHz Pockels Cell polarizer photo- switch spectral filter (computer controlled) - spatial light modulator - acousto-optic modulator Pulse Shaper (A.M. Weiner) Dazzler - FastLite Inc. acousto-optic dispersive filter (P. Tournois et al.) acoustic wave (computer programmable) - spectral amplitude - temporal phase TeO 2 crystal Pulse Amplitude Stabilizer Patent:: LLNL (R. Wilcox) Deformable mirror

John Corlett, July 2004 Laser-driven photocathode - one of the many laser systems H. Tomizawa, JASRIR. Cross, J. Crane, LLNL Need high reliability –Integrated systems –“hot spare” system attractive –Develop techniques for pulse shaping

John Corlett, July 2004 rf gun phase and amplitude LUX rf gun concept as an example Assume 5% of bunch length (1 psec) jitter Primary drivers are launch phase, cell 1 gradient and bunch charge (laser intensity) Assumed uncorrelated disturbances: three most significant parameter tolerances are (rms values): –Launch phase: 0.43 degree –Cell 1 gradient: 1.4% variation –Bunch charge: 36% variation Laser –1 µJ, 35 ps, 10 kHz, 266 nm –Spatial and temporal control to provide low-emittance electron bunches Cathode –Cs 2 Te RF field –64 MVm -1 at cathode

John Corlett, July 2004 Nominal LCLS Linac Parameters for 1.5-Å FEL Single bunch, 1-nC charge, 1.2-  m slice emittance, 120-Hz repetition rate… (RF phase:  rf = 0 is at accelerating crest) SLAC linac tunnel research yard Linac-0 L =6 m Linac-1 L  9 m  rf   25° Linac-2 L  330 m  rf   41° Linac-3 L  550 m  rf   10° BC-1 L  6 m R 56   39 mm BC-2 L  22 m R 56   25 mm LTU L =275 m R 56  0 DL-1 L  12 m R 56  0 undulator L =130 m 6 MeV  z  0.83 mm    0.05 % 135 MeV  z  0.83 mm    0.10 % 250 MeV  z  0.19 mm    1.6 % 4.54 GeV  z  mm    0.71 % 14.1 GeV  z  mm    0.01 %...existing linac new rfgun 21-1b21-1d X Linac-X L =0.6 m  rf =  21-3b24-6d25-1a30-8c P. Emma, SLAC

John Corlett, July 2004 X-band X-X-X-X- Jitter tolerance budget for LCLS based on the many sensitivities rms  t -jitter = 109 fs  z jitter = 14 % rms …and test the budget with jitter simulations Jitter Tolerance Levels in the LCLS Jitter simulation, tracking 10 5 particles 2000 times, where each run is randomized in its 12 main rf-parameters according to the tolerance budget LCLS P. Emma, SLAC

John Corlett, July 2004 SASE FEL output The SASE FEL process arises from noise Radiation intensity build-up along undulator Half way along undulator Saturation

John Corlett, July mm rms 0.1 mm (300 fs) rms Easy access to time coordinate along bunch LCLS BC2 bunch compressor chicane (similar in other machines) x, horizontal pos. (mm) z, longitudinal position (mm) 50  m Slit spoiler defines radiating region of bunch Paul Emma, SLAC

John Corlett, July 2004 Add thin slotted foil in center of chicane 1-  m emittance 5-  m emittance 1-  m emittance AFTER FOIL BEFORE FOIL Paul Emma, SLAC

John Corlett, July 2004 Timing determination from Electro Optic sampling - developing techniques at the SPPS ErEr Principle of temporal-spatial correlation Line image camera polarizer analyzer EO xtal  seconds, 300 pulses:  z = 530 fs ± 56 fs rms  t = 300 fs rms single pulse A. Cavalieri centroid width

John Corlett, July 2004 ESASE - Enhanced Self-Amplified Spontaneous Emission Bunching Acceleration SASE Modulation A. Zholents - Wednesday

John Corlett, July 2004 P 0 = 235 GW With a duty factor = 40, P average ~ 6 GW 70 as Each micro-pulse is temporally coherent and Fourier transform limited Carrier phase is random from micro-pulse to micro-pulse Pulse train is synchronized to the modulating laser L =800 nm x-ray macropulse Enhanced Self-Amplified Spontaneous Emission

John Corlett, July 2004 Dispersive section strongly increases bunching at fundamental wavelength and at higher harmonics In a downstream undulator resonant at 0 /n, bunched beam strongly radiates at harmonic via coherent spontaneous emission nn -n  phase energy --  Input Output e-beam phase space: Energy-modulate e-beam in undulator via FEL resonance with coherent input radiation Harmonic generation scheme - coherent source of soft x-rays L.-H. Yu et al, “High-Gain Harmonic-Generation Free-Electron Laser”, Science (2000) L.H. Yu et al., "First Ultraviolet High Gain Harmonic-Generation Free Electron Laser", Phys. Rev. Let. Vol 91, No. 7, (2003) modulator radiator bunching chicane laser pulse e - bunch Developed and demonstrated by L.-H. Yu et al, BNL

John Corlett, July 2004 seed laser pulse modulator 3rd - 5th harmonic radiator modulator 3rd - 5th harmonic radiator Cascaded harmonic generation scheme Delay bunch in micro-orbit-bump (~50  m) Low  electron pulse Unperturbed electrons seed laser pulse tail head radiator modulator disrupted region

John Corlett, July 2004 User has control of the FEL x-ray output properties through the seed laser OPA provides controlled optical seed for the free electron laser Wavelength tunable – nm Pulse duration variable – fs Pulse energy –10-25 µJ Pulse repetition rate –10 kHz Endstation lasers seeded by or synchronized to Ti:sapphire oscillator –Tight synchronization <20 fs Ti:sapphire Oscillator <100 fs, 2 nJ <50 fs jitter grating stretcher Ti:sapphire Regenerative Amplifier Q-switched Nd:YAG (2  ) grating compressor RF derived from optical from master oscillator ~1 mJ, 800 nm, 10 kHz Optical Parametric Amplifier >10% conv. efficiency e-beam laser seed pulse undulator harmonic n undulator stages x-ray Endstation synch.

John Corlett, July 2004 Gas jet Seeding with XUV from high harmonics in a gas jet (HHG) Coherent EUV generated up to ~ 550 eV –R. Bartels et al, Science 297, 376 (2002), Nature 406, 164 (2000) H. Kapteyn, JILA/Uni. Colorado/NIST E field Harmonic emission Time(fs) I. Christov et al, PRL 78, 1251, (1997) Harmonic order 67.5eV 25.5eV J. Zhou et al, PRL 76(5), (1996)

John Corlett, July 2004 Seeding multiple cascades from a single electron bunch allows 10 kHz operation in LUX concept Optical pulses overlap different part of bunch for each beamline Timing jitter influences number of cascades that can be served by a single bunch CSR effects in the arcs introduce ~ few fs jitter for ~ few % charge variation e-beam FEL optical pulses

John Corlett, July nm spectral broadening and pulse compression e-beam harmonic-cascade FEL two period wiggler tuned for FEL interaction at 800 nm 2 nm light from FEL 2 nm modulator chicane-buncher 1 nm radiator dump end station 1 nm coherent radiation e-beam end station time delay chicane Laser-manipulation produces attosecond x-ray pulses in harmonic cascade FEL e-beam A. Zholents, W. Fawley, “Proposal for Intense Attosecond Radiation from an X-Ray Free-Electron Laser”, Phys. Rev. Lett. 92, (2004)

John Corlett, July 2004 Ultrafast x-ray pulses by electron bunch manipulation and x-ray compression 2 ps ~ 50 fs RF deflecting cavity Electron trajectory in 2 ps bunch

John Corlett, July 2004 Master Oscillator Laser tt tt electron bunch laser pulse x-rays RF crab cavity 3.9 GHz x-ray pulse compression asymmetric Bragg x-tals yy tt yy Low-noise Amp 3.9 GHz Synchronization dependent on phase of deflecting cavity Phase lock to master oscillator Fast feedback systems around scrf Extend frequency response of the system Synchronize deflecting cavities and pump laser for hard x-ray production

John Corlett, July 2004 Typical end station concept Precisely timed laser and linac x-ray pulses Linac x-ray pulse Laser master oscillator pulse End station Pulse diagnostics Laser and delay lines ~ 10 m Modelocked Oscillator Active laser synchronization –Independent oscillators at each endstation –Complete independence of endstation lasers –Wavelength, pulse duration, timing, repetition rate etc.

John Corlett, July 2004 Ti:sapphire Oscillator <100 fs, 2 nJ <50 fs jitter grating stretcher Ti:sapphire Regenerative Amplifier Q-switched Nd:YAG (2w) grating compressor >1 mJ, 800 nm, 10 kHz Optical Parametric Amplifier Beamline endstation lasers PC /4 typical regenerative amplifier ~20 passes   L=1 µm (  t=66 fs) interferometric stabilization cross-correlate with oscillator (compress first) temperature stabilize (Zerodur or super-invar) chirped-pulse amplification RF derived from optical master oscillator

John Corlett, July 2004 All-optical timing system to achieve synchronization between laser pump and x-ray probe Laser-based timing system Stabilized fiber distribution system Interconnected laser systems Active synchronization Passive seeding rf signal generation  20–50 fs synchronization Photo Injector Laser RF cavity Master Oscillator Laser FEL Seed Laser Multiple Beamline Endstation Lasers FEL Seed Laser Linac RF Optical fiber distribution network

John Corlett, July 2004 cw reference laser interferometer L~100 m Path Length Control  L=  2  m  t=  7 fs Agilent 5501B  2  one hour (   2  lifetime Beamline 1 Beamline 2 fiber-based system EDFA (fiber amp) PZT control path length EDFA (fiber amp) Master Oscillator Timing distribution position detector position detector Master Oscillator cw reference laser interferometer Beamline 2 Beamline 1 free-space system (in vacuum)

John Corlett, July 2004 cw reference laser interferometer L~100 m Path Length Control  L=  2  m  t=  7 fs Agilent 5501B  2  one hour (   2  lifetime Beamline 1 Beamline 2 fiber-based system EDFA (fiber amp) PZT control path length EDFA (fiber amp) Master Oscillator Timing distribution - fiber systems developed fro distribution of frequency standards Mixer/amplifier noise floor D. Jones, UCB/JILA

John Corlett, July 2004 Modelocked fiber laser oscillator rf stabilized 28 dB AMP RF Clock 1.3/n GHz Amplifier LPF error signal 17 dBm mixer Modelocked Laser 1.3 GHz T rep BPF 1.3 GHz f 1/T rep Modelocked Fiber Laser Oscillator – RF Stabilized Phase-lock all lasers to master oscillator Derive rf signals from laser oscillator Fast feedback to provide local control of accelerator rf systems  Synchronization 10’s fs

John Corlett, July 2004 Summary Lasers, timing,and synchronization Laser systems under development at many institutions Applications for improved light-source operations Photocathode laser, timing system master oscillator, FEL seed laser, endstation pump laser Manipulation of e - beam by laser has great potential HHG power increasing, wavelength decreasing Ultra-stable timing systems with optical fiber distribution systems under development Application of techniques to accelerator environments and requirements is to be demonstrated 10’s fs synchronization seems achievable