1. Issues and Challenges for Short Pulse Radiation Production
Paul Emma
Stanford Linear Accelerator Center
July 8, 2004

2. -W. Safire, NY Times, March 7, 2004
How Short?
…defined by New York Traffic Commissioner T.T. Wiley in 1950 as:
“…the time between the light turning green and the guy behind you honking.”
-W. Safire, NY Times, March 7, 2004
Several FEL proposals go beyond even this:
sub-femtosecond pulses
1-Å radiation
GW power levels
unprecedented brightness
why so short…

3. used spark photography to freeze this ‘ultra-fast’ process
E. Muybridge at L. Stanford in 1878
disagree whether all feet leave the ground during gallop…
E. Muybridge
used spark photography to freeze this ‘ultra-fast’ process
E. Muybridge, Animals in Motion, ed. L. S. Brown (Dover Pub. Co., New York 1957).

4. Coulomb Explosion of Lysozyme (50 fs)
Single Molecule Imaging with Intense X-rays
Atomic and molecular dynamics occur at the fsec-scale
J. Hajdu, Uppsala U.

5. Time Scales Dt  1 sec 1 femto-second (fs) = 10-15 sec  0.3 m m
1 atto-second (as) = sec  0.3 nm
In Neils Bohr’s 1913 model of the Hydrogen atom it takes about 150 as for an electron to orbit the proton.
– Nature, 2004

6. Outline Electron bunch limitations Photon pulse limitations
Schemes for short pulse generation
SPPS results (Sub-psec Pulse Source)
Just a tick: Scientists are using ever-shorter time scales to investigate chemical reactions.
Nature, February 26, 2004

7. Electron bunch length is limited by…
Coherent synch. rad. (CSR) in compressors
Longitudinal wakefields in linac & undulator
Space-charge forces in accelerator
System jitter (RF, charge, etc)
Try to compress sz in LCLS to 1 mm…
CSR: e /e0 = 1
1 nC
brightness destroyed
CSR: e /e0  14

8. Coherent Synchrotron Radiation in Bendssz e–
Coherent radiation for
lr > sz lr
R (= L/q) R
A. Kabel: MOPKF081 
DE/E = 0 lr
bend-plane emittance is ruined 
DE/E < 0

9. Resistive-Wall Wakefields in Undulator
extreme wake
Copper tube

10. Micro-Bunching Instabilities
FEL ‘instability’ needs very “cold” e- beam (small ex,y & E-spread)
Cold beam is subject to “undesirable” instabilities in accelerator (CSR, Longitudinal Space-Charge, wakefields) t
current modulation 1%
10%
Gain=10
Z(k)
LCLS simulations (M. Borland)
CSR m-bunching
Saldin,
Schneidmiller,
Yurkov
TESLA-FEL
Can be Landau damped with energy spread

11. How cold is the photo-injector beam?
Parmela Simulation
TTF measurement
simulation
measured
M. Hüning, H. Schlarb, PAC’03.
3 keV
DE/E
Dt (sec)
3 keV, accelerated to 14 GeV, & compressed 36  110-5
Too small to be useful in FEL (no effect on FEL gain when <10-4)

12. ‘Laser Heater’ in LCLS for Landau Damping
Ti:saph
800 nm
1.2 MW
Injector at 135 MeV
40 keV rms
‘Laser heater’ suggested by Saldin et al.
Laser-e- interaction  800-nm E-modulation (40 keV rms)
Heater in weak chicane for time-coordinate smearing
Energy spread in next compressors smears m-bunching
Huang: WEPLT156, Limborg: TUPLT162, Carr: MOPKF083

13. In LCLS tracking, final energy spread blows up without ‘Laser-Heater’
heater OFF
0.1%
heater ON
0.01 %
Final longitudinal phase space at 14 GeV for initial 15-mm, 1% modulation at 135 MeV
Z. Huang et al., SLAC-PUB-10334, accepted in PR ST AB, June 2004

14. Outline Electron bunch limitations Photon pulse limitations
Schemes for short pulse generation
SPPS results (Sub-psec Pulse Source)
Just a tick: Scientists are using ever-shorter time scales to investigate chemical reactions.
Nature, February 26, 2004

15. FEL pulse duration limited by intrinsic bandwidth
For shorter pulses:
shorter wavelength, lr
larger r (smaller ex,y)
low-gain (large Dw)
seeded start-up
For X-ray FEL:
lr  1 Å,
sw/w0  0.04%,
st  100 as
FEL-type: Nu Lu
Dw/w
Saturated SASE
~1/r
~20Lg ~r
Seeded High-Gain
<1/r
<20Lg
>r
Seeded Low-Gain
~1/(4pr)
~2Lg
~4pr

16. Monochromator Pulse Slicingw t
sw /h h sw sm
monochromator bandwidth
sm/w0 = 10-4, sw/w0 = 510-4, h  2%  st  5 fs
S. Krinsky, Z. Huang, PR ST AB, 6, (2003).

17. Outline Electron bunch limitations Photon pulse limitations
Schemes for short pulse generation
SPPS results (Sub-psec Pulse Source)
Just a tick: Scientists are using ever-shorter time scales to investigate chemical reactions.
Nature, February 26, 2004

18. HGHG Saturation at DUVFEL
0.9 ps
0.4 ps
0.3 ps
pulse length control with seed laser
266 nm
Li-Hua Yu et al.
PRL 91, (2003).
Ipk = 300 A, sE/E0 = 0.01%
Pin = 1.8 MW: sz = 0.6 ps, ge = 2.7 mm, dy/dg = 8.7
Pin = 30 MW: sz = 1.0 ps, ge = 4.7 mm, dy/dg = 3.0

19. Statistical Single-Spike Selection
Un-seeded single-bunch HGHG (8  4  2  1 Å )
8 Å
I8  I18
1 Å
300 as
Saldin et al., Opt. Comm., 212, 377 (2002).

20. e- Add thin slotted foil in center of chicane y 2Dx x  DE/E  t
coulomb scattered e-
unspoiled e-
2Dx
x  DE/E  t
15-mm thick Be foil
LCLS
PRL 92, (2004).
P. Emma, M. Cornacchia, K. Bane, Z. Huang, H. Schlarb, G. Stupakov, D. Walz (SLAC)

21. 200 fs DE/E No design changes to FEL – only foil added in chicane
Track 200k macro-particles through entire LCLS up to 14.3 GeV
200 fs
DE/E
cold e- core passing through slot
No design changes to FEL – only foil added in chicane

22. 2 fs FWHM Power (GW) z  60 m ~1010 photons x-ray Power
Genesis 1.3 FEL code
~1010 photons
x-ray Power
2 fs FWHM
(<1 fs possible)
Power (GW)

23. 800 nm
2 nm, 100 MW, 100 fs
Mod. tuned so only high energy e- interact with 2-nm HC FEL radiation
Modulator
Chicane
2 nm
LUX electron beam parameters:
e- energy = 3 GeV
emittance = 2 mm-mrad
energy spread = 0.3 MeV
peak current = 500 A
~2x106 photons
110 as
1 nm
Generation of Attosecond Pulses…
A. Zholents, W. Fawley
PRL 92, (2004).
MOPKF072

24. 300 as 1 GW Saldin et al., Opt. Comm., 237, 153 (2004). Ge
Ti:saph: 800 nm, 2-4 mJ, 5 fs
300 as
monochromator to select single pulse
monochromator is broadband Ge crystal diffracting from the (1 1 1) lattice planes
(pre-monochromator to reduce power)
1 GW
Saldin et al., Opt. Comm., 237, 153 (2004).

25. E-SASE (applied to LCLS)
SASE FEL
4 GeV
14 GeV
800-nm modulation (few GW)
short pulse train
peak current enhanced x7
70 as
24 kA
Allows synchronization between laser pulse and x-ray pulse
E-SASE (applied to LCLS)
A. Zholents
(submitted to PRL)

26. Outline Electron bunch limitations Photon pulse limitations
Schemes for short pulse generation
SPPS results (Sub-psec Pulse Source)
Just a tick: Scientists are using ever-shorter time scales to investigate chemical reactions.
Nature, February 26, 2004

27. Short Bunch Generation in the SLAC Linac
1-GeV Damping Ring
sz  6 mm
SLAC Linac
FFTB
add 14-meter chicane in linac at 1/3-point (9 GeV)
sz 1.1 mm
sz  40 mm
Existing bends compress to 80 fsec
1.5 Å
compression by factor of 500
30 GeV
sz  12 mm
1.5%
28.5 GeV
30 kA
80 fs FWHM
P. Emma et al., PAC’01

28. Source comparisons SPPS 11025 80 2107 2106 1109 500 1106 100
Peak
brightness**
Pulse length (fsec)
Average flux (photon/sec)
Photons per pulse per 0.1% BW
Rep. Rate (Hz)
Table top
laser plasma
1109
500
1106
100
1104
ALS* (streak camera)
51017
4104
2108
2104
ALS slicing (undulator)
11017
(61019)
1105
(3104) 10
(300)
ESRF
11024
8104
31010
3107
900
SPPS
11025 80
2107
2106
* streak camera resolution 1 psec, DQe 0.01
** photons/sec/mm2/mrad2/0.1%-BW
J. Hastings, SLAC

29. Dave Fritz, Soo Lee, David Reis
Undulator,
view upstream
Dave Fritz, Soo Lee, David Reis
Undulator parameters: Lu  2.5 m, lu = 8.5 cm, K  4.3, B  0.55 T, Np  30

30. R&D at SPPS Towards X-Ray FELs
 Measure wakefields of micro-bunch
 Develop bunch length diagnostics
 Study RF phase stability of linac
 Measure emittance growth in chicane (CSR)
 X-ray optics and transport

31. Wakefield energy-loss used to set and confirm minimum bunch length
sz  40 mm
theory
meas.
K. Bane et al., PAC’03

32. Transition radiation is coherent for /2p > sz (CTR)
P. Muggli, M. Hogan

33. CTR sz  9 mm Gaussian bunch: sz  18 mm
minimum bunch length (with j-jitter)
Mylar
resonances
CTR
Autocorrelation
Gaussian bunch: sz  18 mm
sz  9 mm
Dz (mm)
P. Muggli, M. Hogan

34. SPPS chicane CSR simulations with 1D model (unshielded)
(good agreement with 3D-model studied by F. Stulle - DESY)
3.4 nC, 9 GeV
9 kA
1 mm
FWHM/2.35  40 mm
0.3 kA

35. Bend-Plane Emittance: Chicane ON and OFF
Bend-plane emittance is consistent with calculations and sets upper limit on CSR effect
P. Emma et al., PAC’03

36. Concluding Remarks
Very short x-ray pulses are key to exploring ultra-fast science at future light sources
Linac-based FEL’s offer high power, very high brightness, and possibly sub-femtosecond pulses at ~1-Å wavelengths
Advances in ultra-short, high-power table-top lasers will greatly influence future LS designs, as will e- gun development (gex,y < 1 mm)
Thanks to the many who contributed to this presentation…
Z. Huang, W. Fawley, and A. Zholents