1 zholents, 03-09-2011 the quest for ultra-short x-ray pulses alexander zholents anl fermilab,...

1 Zholents, 03-09-2011 The Quest for Ultra-Short X-ray Pulses Alexander Zholents ANL Fermilab, 03/09/2011

2 Zholents, 03-09-2011 J. Levesque and P.B. Corkum, Can. J. Phys. 84: 118 (2006) 2010 shorter and shorter laser pulses were obtained since discovery of mode locking in 1964. Each advance in technology opened a new field of science and each advance in science strengthened the motivation for even shorter laser pulses. Thomson Slicing SPPS LCLS X-ray pulses Expected

3 Zholents, 03-09-2011 Scientific drivers. Why ultra-short pulses? Phase transitions in solids Surface dynamics Making and braking of bonds during chemical reactions Chemical dynamics in proteins Correlated behavior of electrons in complex solids for showing that it is possible with rapid laser technique to see how atoms in a molecule move during a chemical reaction ~1 / (speed of sound) ~ 100 fsFemtochemistry Ahmed Zewail, Nobel Prize, 1999 The vibration period between the two hydrogen atoms in a hydrogen molecule is about 8 fs

4 Zholents, 03-09-2011 Molecule of rhodopsin before C H N 1) R.W. Schoenlein, L.A. Peteanu, R.A. Mathies, C.V. Shank, Science, 254, 412 (1991). and after absorption of a photon First step in vision 1) How living systems function using smallest amount of energy?

5 Zholents, 03-09-2011 Charles Shank In 1981 Charles Shank and coworkers at Bell Labs redefined the term ultrafast when they reported the demonstration of 90 fs long pulses from colliding-pulse dye laser 1 1) R.L. Fork, B.I. Greene, C.V. Shank, Appl. Phys. Lett., 38, 671(1981). Probe valence electrons with optical laser Probe core electrons with x-rays

6 Zholents, 03-09-2011 Laser assisted techniques: 90 o Thomson scattering 1 1) S. Chattopadhyay, K.-J. Kim, C. Shank, Nucl. Instr. Meth., A341, 351 (1994). 2) R.W. Schoenlein et. al., Science, 274(11), 236 (1996). 300 fs

7 Zholents, 03-09-2011 90 o Thomson scattering (2) 300 fs 1) A.H. Chin, R.W. Schoenlein, T.E. Glover, P. Balling, W. P. Leemans, C. V. Shank, Ultrafast Structural Dynamics in InSb Probed by Time-Resolved X-Ray Diffraction, Phys. Rev. Lett. 83, 336 - 339 (1999). Lattice expansion dynamics in InSb as a function of time delay between laser and x-ray pulses 1 X-ray probe before the laser pump X-ray probe after the laser pump

8 Zholents, 03-09-2011 Femtosecond X-ray Beamline First Light 2000 In-vacuum Undulator Femtosecond Laser ~50 W Slicing source of fs x-ray pulses at the ALS 1 1) R.W.Schoenlein et al, Science, March 24, (2000) wiggler 100 fs electron slice undulator beamline 70 ps electron bunch 100 fs laser pulse spatial separation by dispersive bend W Laser - ebeam interaction in wiggler 100 fs x-ray pulse synchronous to laser

9 Zholents, 03-09-2011 Electron trajectory through wiggler Wiggler period Magnetic field in the wiggler BB 0 sin( k u z ) Laser wavelength FEL resonance condition While propagating one wiggler period, the electron is delayed with respect to the light on one optical wavelength = Light interaction with relativistic electron *) E k B E k B V V E laser N S S N S S N N e - u light *) Motz 1953; Phillips 1960, Madey 1971 Energy modulation of electrons in the wiggler magnet by the laser light energy modulation over the length of one optical cycle

10 Zholents, 03-09-2011 Interference term defines energy gain/loss Alternative approach to find energy modulation Far field observer Far field observer sees the field: laser spontaneous emission laser Electron beam

11 Zholents, 03-09-2011 Selection of fs x-ray pulses EEEE z 100 fs 2E2E Electron beam energy modulation XXXXz 100 fs 2x2x In dispersiv e place X=D E/E Radiation of these electrons is selected

12 Zholents, 03-09-2011 Other means to select fs pulse besides coordinate separation spectral selection (works only with undulator source) 2 Bandwidth of the undulator radiation at a high harmonic number n 1) R.W. Schoenlein, et al., Appl. Phys. B71, 1 (2000). 2) H. Padmore, private discussion Selection of fs x-ray pulses 1 time-off-flight selection -- ++ angular selection wigglerundulator bend magnet electron bunch laser pulse subps x-ray pulse mask BESSY: courtesy S. Khan Select before first x-ray mirror

13 Zholents, 03-09-2011 bend magnet visible radiation Ti:Sa laser Ti:Sa amplifier BBO e-e- slit h 2 = ~2 eV h 1 = 1.55 eV h =h 1 +h 2 Measurement of a short pulse of synchrotron radiation via cross- correlation with a short laser pulse intermediate focus PMT filter e-beam fs pulse light Diagnostics -60-40-2002040 60 0 50 100 150 200 250 300 350 # photons delay (ps) = 16.6 ps

14 Zholents, 03-09-2011 -1200-1000-800-600-400-2000 200 60 80 100 120 140 160 180 delay (fs) counts -1200-1000-800-600-400-2000200 100 150 200 250 counts -1500-1000-50005001000 1500 2000 2500 counts Electron Density Distribution time (ps)0.3-0.3 x/ x +3 x to +8 x +4 x to +8 x -3 x to +3 x Diagnostics (2) ALS bend magnet beamline Modulation amplitude extracted from experimental data is 6.4 MeV (expected ~ 10 MeV)

15 Zholents, 03-09-2011 Diagnostics (3) Electron loss rate versus scraper position Deducing energy modulation amplitude from beam lifetime measurements using scraper in dispersive location (BESSY) Energy modulation amplitude versus laser pulse energy Approximately two times more laser pulse energy was used than it was predicted (same problem at ALS) Not explained so far ! theory experiment laser pulse energy, (mJ) without laser with laser courtesy S. Khan scraper position, (mm)

16 Zholents, 03-09-2011 Slicing at BESSY 1) x-ray pump pulse e 1) S. Khan, et al., PRL, 97, 074801 (2006) Detected photon rate per 0.1% bandwidth versus cutoff angle photons/(s 0.1% bw) signal-to-background with laser without laser signal/background angle, (mrad)

17 Zholents, 03-09-2011 1 2 wiggler detuning form FEL resonance Gain, % I 25A bunch train and a gap Measurement of FEL gain through wiggler at ALS Small-signal FEL gain Madeys theorem FEL gain ~ laser spectrum gain function laser e-beam 0.4 0.2 measured with laser oscillator FEL resonance -60-40-20020406080 0 1 2 3 4 5 gain (x10 -3 ) delay (ps) electron bunchlaser pulse = 16.6 ps Gain follows peak current distribution

18 Zholents, 03-09-2011 first turn second turn 1.2 time (ps) frequency (THz) Relative charge density Amplitude (arb. units) 0.4 1.04 0.92 Laser-induced coherent fs THz radiation 1-4 e-beam density distribution Dip in the electron density distribution expands and dries out as the electron bunch travels along the ring e-beam density distribution time (ps)0.3-0.3 x/ x 1)R.W.Schoenlein et al, Appl. Physics, B71, 1 (2000). 2)J. Byrd et al, Phys. Rev. Lett., 96, 164801(2006). 3)K. Holldack et al, Phys. Rev. Lett., 96, 054801 (2006). 4)J. Byrd et al, Phys. Rev. Lett., 97, 074802 (2006). Large, medium and small modulation amplitudes

19 Zholents, 03-09-2011 Dip reconstruction from THz spectra 1 1) K. Holldack et al, Phys. Rev. Lett., 96, 054801 (2006). wave number, (1/cm) time, (ps) P coh /P inc, (arb. units) electron density, (arb. units) THz signal is now routinely used for tuning of laser e-beam interaction and to maintain it with a feedback on mirrors BESSY, ALS, SLS

20 Zholents, 03-09-2011 Black: measurement Red: theoretical fit Alternative approach to find energy modulation* Laser Spontaneous emission An example of a poor overlapping: wiggler is detuned too far away from the laser frequency *) A. Zholents, K. Holldack, Proc. FEL06, Berlin (2006). In the experiment, wiggler gap was adjusted such as to change the central frequency of spontaneous emission from 200 nm to 1000 nm laser

21 Zholents, 03-09-2011 1)A. Zholents, P. Heimann, M. Zolotorev, J. Byrd, NIM A, 425, 385 (1999). 2)M. Katoh, Japan. J. Appl. Phys, 38, L547(1999) Radiation from tail electrons angle >> beam divergence + x-ray diffraction Radiation from head electrons undulator Storage Ring Deflecting cavity delivers a time-dependent vertical kick to the beam Compression using asymmetrically cut crystal Trading brightness to a short pulse Ideally, second cavity cancels effect of first cavity ~1 ps High repetition rate source of ps x-ray pulses 1,2

22 Zholents, 03-09-2011 Application to the Advanced Photon Source 1 Part of the APS upgrade pursued in an active collaboration with JLab Pulse length versus transmission through aperture calculated for 10 keV photons courtesy M. Borland 6 MV deflection rf harmonic number Obtaining short x-ray pulses at APS 1-3 1) K. Harkay et al, Proc. PAC05, 668(2005). 2) M. Borland, Phys. Rev. ST AB, 8, 074001(2005). 3) M. Borland et al, Proc. PAC07, (2007). diffraction limited Pulse length versus photon energy emittance limited saturated at rf kick

23 Zholents, 03-09-2011 Synchronization between laser pump and x-ray probe pulses LASER OSCILLATOR (passively modelocked) tt tt 3.0 GHz (RF Kick) electron bunch laser pulse x-rays Synchronous bunch Jitter in the e-beam arrival time is converted into position jitter of compressed x-ray pulse Early bunch Asymmetrically cut crystal Late bunch Sensitivity to electron bunch timing jitter is significantly reducedaperture or intensity jitter behind the aperture

24 Zholents, 03-09-2011 add 14-meter chicane in linac at 1/3-point (9 GeV) 1-GeV Damping Ring z 1.1 mm z 40 m z 12 m z 6 mm SLAC Linac 30 GeV 30 GeV FFTB Short Bunch Generation with the SLAC Linac - SPPS Existing bends compress to 80 fsec Existing bends compress to 80 fsec 1.5 compression by factor of 500 P. Emma et al., PAC01 1.5% 28.5 GeV 80 fs FWHM 30 kA measurement < 300fs Single pass, low rep. rate

25 Zholents, 03-09-2011 New Scientists Coherent emission of x-rays using Free Electron Lasers: a road to attosecond x-ray pulses 2

Zholents, Avalon, 10/2010 E. Goulielmakis et al., Nature, 466, 739(2010). Probing intra-atomic electron motion by attosecond absorption spectroscopy. 80 attoseconds ! June 19, 2008 Attosecond XUV pulses had been obtained

27 Zholents, 03-09-2011 Attosecond x-ray pulses is a powerful tool for addressing Grand Challenges in Science and BES Research Needs How do we control materials and processes at the level of electrons?How do we control materials and processes at the level of electrons? How do we design and perfect atom-and energy-efficient synthesis of new forms of matter with tailored properties?How do we design and perfect atom-and energy-efficient synthesis of new forms of matter with tailored properties? How do remarkable properties of matter emerge from complex correlations of atomic and electronic constituents and how can we control these properties?How do remarkable properties of matter emerge from complex correlations of atomic and electronic constituents and how can we control these properties? Can we master energy and information on the nanoscale to create new technologies with capabilities rivaling those of living systems?Can we master energy and information on the nanoscale to create new technologies with capabilities rivaling those of living systems? How do we characterize and control matter awayespecially very far awayfrom equilibrium?How do we characterize and control matter awayespecially very far awayfrom equilibrium? 2007 G. Fleming

Zholents, Avalon, 10/2010 Short EUV/x-ray pulses are routinely produced at FLASH (10 70 fs), SCSS (~ 30 fs), LCLS (

SUB-FEMTOSECOND X-RAY PULSES USING THE SLOTTED FOIL METHOD P. Emma, M. Cornacchia, K. Bane, Z. Huang, H. Schlarb,G. Stupakov, D. Walz, PRL, 2004 BC2 4.3 GeV 14 GeV BC1 250 MeV 135 MeV gun 4 wire scanners to FEL h =8 keV Linac Coherent Light Source, SLAC 200 fs 7 MeV Only bright spot will lase z EE energy chirp X-ray pulse width ~ 400 asec Bunch arrival time jitter ~ 50 fs ~ 10 9 photons/pulse -> 7 GW Courtesy P. Emma Simulation using Elegant

time (fs) Power (GW) 0105 0-150 fs 2 fs 2-Pulse Production with 2 slots 0-6 mm 0.25 mm pulses not coherent Double X-Ray Pulses from a Double- Slotted Foil Courtesy P. Emma FEMTOSECOND X-RAY PULSES IN THE LCLS USING THE SLOTTED FOIL METHOD Precise controlled time delay between x-ray pump and x- ray probe pulses

Slotted Foil in at -6000 um Slotted Foil in at -34000 um Slotted Foil in at -37000 um Over-compressed bunch introduces e - energy chirp on dump screen ~time ~time ~time time dumpscreen single slot double slot HEAD TAIL Courtesy P. Emma Initial results (very preliminary), June 17, 2010 X-ray pulse energy slotse-bunch Wider slot gives more energy

Zholents, Avalon, 10/2010 Pump probe studies using ultra-fast x-ray pulses Stop-motion photography E. Muybridge, 1878 Pellet hits a strawberry delay x-ray probe visible pump

36 Zholents, 03-09-2011 Options for experiment utilizing synchronized pump and probe signals when electron bunch arrival time has a large jitter Chicane Undulator IR pump, ~100 MW X-ray probe Single color x-ray pump x-ray probe experiment Split single x-ray pulse into two and adjust delay Split single x-ray pulse into two and adjust delay Create pump signal using cohrent undulator radiation and Create pump signal using cohrent undulator radiation and adjust delay 1 (in case of an ultra-short e-bunch, ~ 1 fs) adjust delay 1 (in case of an ultra-short e-bunch, ~ 1 fs) 1 ) U. Fruhling et al., Nature photonics, 3, 523(2009); F. Tavella et al., Nature photonics, 5, 162(2011) Use double slotted foil Use double slotted foil

37 Zholents, 03-09-2011 Precision synchronization of pump and probe pulses Seeded FELs naturally posses precise synchronization Seeded FELs naturally posses precise synchronization if electron bunch length > laser pulse + jitter if electron bunch length > laser pulse + jitter Current-enhanced SASE FEL --> same conclusion (Zholents, 2004) Current-enhanced SASE FEL --> same conclusion (Zholents, 2004) Bunching AccelerationModulation Peak current t 20-25 kA 10 fs After bunching This part will lase ~50 fs lasere-bunch 10 fs Require synchronization of the seed and pump lasers 1) 1)J. Kim et. al., 1)J. Kim et. al., Nature Photonics, 2, 733, 2008; R. Wilcox R. Wilcox, Opt. Lett. 34, 3050, 2009

38 Zholents, 03-09-2011 e-beam ~ 50 fs Laser pulse ~ 5 fs Attosecond pulse generation via electron interaction with a few cycle carrier-envelop phase stabilized laser pulse Basic idea: Take an ultra-short slice of electrons from a longer electron bunch to produce a dominant x-ray radiation Small jitter in the electron bunch arrival time is not important good for pump- probe experiments using variety of pump sources derived from initial laser signal

39 Zholents, 03-09-2011 Electron trajectory through wiggler Wiggler period Laser wavelength Fragment of the electron bunch While propagating one wiggler period, the electron is delayed with respect to the light on one optical wavelength Light interaction with relativistic electron E k B E k B V V E laser N S S N S S N N e - u light Laser pulse: 1 mJ, 5-fs at 800 nm wave length with CEP stabilization EE Sin-wave Cos-wave

40 Zholents, 03-09-2011 Energy modulation induced in the electron bunch during interaction with a ~1 mJ, 5 fs, 800 nm wave length laser pulse in a two period wiggler magnet with K value and period length matched to FEL resonance at 800 nm Current enhancement Peak current This spike gives a dominant signal

41 Zholents, 03-09-2011 Energy modulation of electrons produced in interaction with two lasers Current enhancement method *) Combined field of two lasers: increases one laser bandwidth t (fs) Electric field *) Zholents, Penn, PRST-AB, 8, (2005); Phys. Rev. ST-AB, 12, (2009). Y. Ding et al., Phys. Rev. ST-AB, 12, (2009). 800 1000 nm laser; 7.5 25 fs; 0.2 0.5 mJ Undulator with ~ 1% taper 1300 1600 nm laser; 10 45 fs; 0.07 0.2 mJ

42 Zholents, 03-09-2011 one laser two lasers Selection of attosecond x-ray pulse: regions with higher peak current reach saturation earlier Contrast 1 (assuming 100 fs long bunch ) Nearly Fourier transform limited pulse t (fs) current, (kA) t (fs) 10 J 10 10 ph Power, (GW) 250 asec X-ray wavelength = 0.15 nm Current enhancement method (2)

43 Zholents, 03-09-2011 [1] A. A. Zholents and W. M. Fawley, Phys. Rev. Lett. 92, 224801 (2004). [2] E.L. Saldin, E.A. Schneidmiller, M.V. Yurkov, Opt. Commun. 237,153 (2004). [3] E.L. Saldin, E.A. Schneidmiller, M.V. Yurkov, Opt. Commun. 239,161 (2004). [4] A. A. Zholents and G. Penn, Phys. Rev. ST-AB 8, 050704 (2005). [5] E.L. Saldin, E.A. Schneidmiller, M.V. Yurkov, Phys. Rev. ST-AB 9, 050702 (2006). [6] A. A. Zholents and M.S. Zolotorev, New J. Phys. 10, 025005 (2008). [7] W.M. Fawley, Nucl. Inst. and Meth. A 593, 111(2008). [8] Y. Ding, Z. Huang, D. Rather, P. Bucksbaum, H. Maerdji, Phys. Rev. ST-AB 12, 060703 (2009). 060703 (2009). [9] D. Xiang, Z. Huang, G. Stupakov, Phys. Rev. ST-AB 12, 060701 (2009). [10] A. A. Zholents and G. Penn, Nucl. Inst. and Meth. A 612, 254(2010). Publications exploring generation of attosecond x-ray pulses using a few-cycle laser pulse with a carrier envelop phase stabilization:

Zholents, Avalon, 10/2010 ~ 200 as Contrast 1 Energy modulation x =0.15 nm Tapered undulator method 1 Energy chirp is compensated by the undulator taper in the central slice 1) E.L. Saldin, E.A. Schneidmiller, M.V. Yurkov, Phys. Rev. ST-AB 9, 050702 (2006). Frequency chirp definition Wigner transform of the on-axis far field -2.50-5 t, fs 7.9 7.6 7.8 Wavelength, nm Chirp 0.5 7.7 2.5 W.M. Fawley, Nucl. Inst. and Meth. A 593, 111(2008). Fourier transform limited pulse ~ 1.5 fs (FWHM) Hard x-rays Soft x-rays With two laser one can manipulate the energy chirp and, thus, the frequency chirp

Zholents, Avalon, 10/2010 Photoelectron probability Photoelectron momenta Sudden photoionization creates a coherent superposition of electronic states, G. Yudin, PRL, (2006) The figure-of-merit is broad bandwidth of attosecond pulses

Zholents, Avalon, 10/2010 Artists (Denis Han) view of excited electron wavepackets in molecule created by core excitation with attosecond x-ray pulses (courtesy S. Mukamel) Intense attosecond x-ray pulses from FELs provide the opportunity to probe the matter on atomic scale in space and time Stimulated X-ray Raman spectroscopy *) X-ray pump, X-ray probe; element specific energy v-band EFEF core level photon in photon out E~10eV h out, k out 300 asec -> 6 eV, i.e. sudden excitation reveals multi-electron dynamics *) Schweigert, Mukamel, Phys. Rev. A 76, 012504 (2007) In molecules all electrons move in a combined potential of ion core and other electrons

2 m laser TEM 00 TEM 10 Selection of attosecond x-ray pulses via angular modulation of electrons *) *) Zholents, Zolotorev, New Journal of Physics, 10, 025005 (2008). Hermite-Gaussian laser modes 2 m laser

10 -10 P x-ray (W) t (fs) X-ray peak power as a function of time Combining angular and energy modulations for improved contrast of attosecond x-ray pulses 100 GW 115 as, 10 J ~100mJ/cm 2 Central peak Contrast > 100 X-ray wavelength = 0.15 nm

Obtaining attosecond pulses at 1 nm using echo effect *) *) D. Xiang, Z. Huang, G. Stupakov, Phys. Rev. ST-AB 12, 060701 (2009). Adding energy chirp via interaction with ultra short laser pulse; needs sub-fs synchronization radiator has only 12 periods x-ray pulse 20 asec

wiggler1 chicane1 radiator1wiggler2wiggler3radiator2 chicane2chicane3 Two color attosecond pump and attosecond probe x-ray pulses *) TTTT *) Zholents, Penn, Nucl. Inst. and Meth. A 612, 254(2010). z/ E/ E Fragment of the longitudinal phase space z/ E/ E Adjustable time delay with better than 100 asec precision zoom Zoom into the main peak shows microbunching at 2.28 nm TTTT =410 eV =543 eV

7.2 eV FWHM 6.4 eV FWHM 543 eV 210 asec FWHM 410 eV 480 asec FWHM TT Simulation results using 1D code and GENESIS for two color scheme time, (fs) photon energy, (eV) adjustable Molecule structure of 5-quinolinol

Zholents, 03-09-2011 52 Three synchrotron light sources ALS, BESSY, SLS routinely operate with 100 200 fs x-ray pulses Three synchrotron light sources ALS, BESSY, SLS routinely operate with 100 200 fs x-ray pulses SOLEIL, SPring8, APS pursuing plans to add ulrafast x-ray science capacities SOLEIL, SPring8, APS pursuing plans to add ulrafast x-ray science capacities X-ray FELs FLASH, SCSS and LCLS routinely work with ultra-short XUV/x-ray pulses. X-ray FELs FLASH, SCSS and LCLS routinely work with ultra-short XUV/x-ray pulses. Summary

53 Zholents, 03-09-2011 Summary: FELs the light fantastic We are at the threshold of a new era of science, where for the first time, the new instruments, the x-ray FELs, are capable to study the matter with a single atom time and space resolution. Remarkably, adding attosecond capabilities to existing FELs require rather modest modifications. P. Bucksbaum, Science, 317, 766(2007). Conical intersection pump Attosecond probe Expected soon: X-ray pulses million times brighter and thousand times shorter than anything can be done using spontaneous emission

54 Zholents, 03-09-2011 Acknowledgement I greatly benefited from discussions with many people including: M. Borland,J. Byrd, J. Corlett, P. Emma, W. Fawley, E. Glover,P. Hiemann,K. HolldackZ. Huang, S. Khan,M. MartinB. McNeil, C. Pellegrini, G. Penn, V. Sajaev,F. Sannibale, R. Schoenlein,J. Staples, G. Stupakov, M. Venturini, J. Wurtele, M. Zolotorev M. Borland, J. Byrd, J. Corlett, P. Emma, W. Fawley, E. Glover, P. Hiemann, K. Holldack, Z. Huang, S. Khan, M. Martin, B. McNeil, C. Pellegrini, G. Penn, V. Sajaev, F. Sannibale, R. Schoenlein, J. Staples, G. Stupakov, M. Venturini, J. Wurtele, M. Zolotorev,

Zholents, Avalon, 10/2010 Thank you for your attention

Zholents, Avalon, 10/2010 Back-up slides

57 Zholents, 03-09-2011 Recent studies show that a smaller emittance (by a factor of 10), and very short, ~ 1 fs or less, electron bunches can be produced if the electron bunch charge is dropped to 1 -10 pC Ultra-short X-ray pulses with low charge electron bunches 1- 10 pC *) UCLA J.B. Rosenzweig et al., NIM A 593, 39 (2008); *) J.B. Rosenzweig et al., NIM A 593, 39 (2008); C. Pellegrini, seminar at LBNL, 07/11/08 C. Pellegrini, seminar at LBNL, 07/11/08 peak current Normalized slice emittance Slice energy spread Electron beam brightness can be increased by a factor 10 - 100 Road to compact FELs

58 Zholents, 03-09-2011 Example of simulations for LCLS with 1 pC *) J.B. Rosenzweig, talk at FEL workshop, LBNL, November 2008 *) J.B. Rosenzweig, talk at FEL workshop, LBNL, November 2008 Improved brightness -> reduced saturation length saturation at ~70 m ~350 asec Difficult to synchronize to external source due to electron bunch arrival time jitter

59 Zholents, 03-09-2011 *) Saldin, Schneidmiller, Yurkov, Optics, Com., 239 (2004) + seed signal interacts with virgin electrons in the second undulator second undulator is tuned to favor SASE for electrons at the offset frequency 0 + Contrast >> 1 (assuming 100 fs long electron bunch) no saturation ~300 asec, ~5-25 J Attosecond x-ray pulse Spectral separation plus seeding *) seed + X-ray wavelength = 0.15 nm Selection of attosecond x-ray pulse

60 Zholents, 03-09-2011 Echo effect for harmonic generation of x-rays *) E/ E z/ *) G. Stupakov, PRL, 102, 074801(2009). FEL undulator

1 zholents, 03-09-2011 the quest for ultra-short x-ray pulses alexander zholents anl fermilab,...

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