Transcript Timing using an Enhanced SASE technique

Timing Controls Using Enhanced SASE Technique*)
A. Zholents
*)
or
towards absolute synchronization between “visible” pump and
x-ray probe pulses
SLAC XFEL short bunch measurement and timing workshop
July 26 – 30, 2004
A. Zholents, July 28, 2004
Pump-probe experiment concept
X-ray probe pulse
Laser excitation pulse
sample
X-ray
detector
∆t
ion or edetector
• Requires control/measure of Dt with a resolution better than
x-ray pulse duration (possibly as small as 100 attoseconds)
A. Zholents, July 28, 2004
Pump-probe experiment concept
con’t
Multicolor excitation
sample
X-ray probe pulse
X-ray
detector
ion or edetector
A. Zholents, July 28, 2004
Pump-probe experiment concept
con’t
• One can hope to get a required synchronization if all
sources are linked to a common origin
controlled delay
Master
laser
source
Near IR
XUV
Courtesy
H. Kapteyn
laser - e-beam X-ray probe pulse
manipulation
and “seeding”
• 90o Thomson scattering:
• “Slicing”:
• Harmonic Cascade FEL:
Schoenlein, R.W., et al., Science, 274, (1996)236.
Schoenlein, R.W., et al., Science,. 287, (2000 )2237.
L.-H. Yu, et al., Science, 289, (2000)2237.
A. Zholents, July 28, 2004
Enhanced Self Amplified Spontaneous Emission (ESASE)
Master source
Near IR pump
Energy modulation in the
wiggler at 2 - 4 GeV
Required:
•Laser peak power ~ few GW
•Wiggler with 10 – 20 periods
Assumed:
•Electron energy spread ~ 1.2 MeV
Only one optical cycle is shown
A. Zholents, July 28, 2004
Acceleration to 14.35 GeV and bunching at the laser wavelength
Dz  lL / 2B
50 fs laser pulse
lL= 2 microns
z /lL
Energy spread
Peak current
Only one optical cycle is shown
bunching
Peak current
acceleration
A. Zholents, July 28, 2004
Peak current and energy distribution within one micro-bunch
SASE in the undulator producing x-rays synchronized to the
modulating laser
The output x-ray radiation from a single micro-bunch
Dz x  Dz / 2Ln 8  Mˆ G lx
70 as
Power at saturation (estimate for bunching~0.5), P0~200 GW
• Each spike is nearly temporary coherent and Fourier transform limited.
• Carrier phase for an x-ray wave is random from spike to spike.
A. Zholents, July 28, 2004
Peak power
The x-ray radiation output from the entire electron bunch
z /lL
Shaping of a temporal profile of the laser pulse is a tool
for shaping of a temporal profile of the x-ray pulse.
A. Zholents, July 28, 2004
e-beam based timing reference
Master source
Near IR pump
Near IR pump
ESASE
one period
isochronous wiggler
bend
wiggler radiation,
x-rays
~0.5 GW
SH
correlator
A. Zholents, July 28, 2004
laser pulse, I1(t)
Single shot measurement of a time jitter
using Second Harmonic intensity correlation
F. Salin, et al., Applied Optics, 26, (1987)4528
filter
wiggler pulse, I2(t)
KDP
detector
I1(t)
x
w0
SH
2w0
2F

S(x) =
 I t   I t   dt
1
2

w0
n x sin F

c
KDP
~0.3 mm I2(t)
A. Zholents, July 28, 2004
Demonstration of the detector calibration by inserting 0.36 mm glass plate in either arm.
(from C. Rempel and W. Rudolph, Experimentell Technik der Physic, 37, (1989)381.)
A. Zholents, July 28, 2004
Summary
1) Synchronization between pump and probe pulses is
obtained by linking all pulses to the common origin.
2) ESASE provides a time mark for the x-ray pulse and allows
absolute synchronization between laser pulse and x-ray pulse.
3) ESASE allows control over the duration of x-ray pulse and
its temporal shape. X-ray pulses less than 100 attoseconds
are feasible.
4) ESASE allows beam based monitoring for a time jitter
with better than fs resolution.
A. Zholents, July 28, 2004