Transcript Technical Talk: Seeding for Fully Coherent Beams

Seeding for Fully Coherent Beams
William S. Graves
MIT-Bates
Presented at MIT x-ray laser user
program review
July 1, 2003
W.S. Graves
1
Outline
•Bandwidth and pulse length
•Terminology
•High Gain Harmonic Generation
•Facility layout, experimental halls, beamlines
•Plans for short wavelength seed generation
•Simulations of seeded x-ray performance
•Femtosecond timing
•Source parameter summary
W.S. Graves
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Bandwidth and Pulse Length
Seeded beam
SASE beam
Output
wavelength
FEL param
rFEL
Dtmin (fs) at
max BW
DEmin (meV) at
1 ps FWHM
SASE Dtmin
(fs)
SASE DEmin
(meV)
100 nm
9.e-3
20
2
100
110
10 nm
4.e-3
5
2
100
500
1 nm
1.5e-3
1
2
100
1900
0.1 nm
0.2e-3
0.8
2
100
2500
Data from BNL’s
Seeded beams limited only by
DUV-FEL experiment
uncertainty principle and seed
1
Df Dt 
2
properties.
SASE properties determined
by ebeam.
W.S. Graves
Df
f
 rFEL
3
Terminology
•SASE: self amplification of spontaneous emission. Electron beam amplifies initial spontaneous undulator
radiation. Transverse coherence, but not longitudinal.
•Seeded beams: A coherent laser pulse is introduced at the undulator entrance. The seed power must
dominate the initial undulator radiation.
•Self-seeding: In a 2-part undulator, radiation from the first section seeds the FEL process in the second
section.
•HHG: High-harmonic generation. A method of generating pulses of ~10 nm light by focusing a Ti:Sapp
laser in a gas jet.
•HGHG: High-gain harmonic generation. A method of frequency multiplying an input seed laser to reach
a shorter output wavelength.
•Cascaded HGHG: Multiple stages of HGHG to reach ever shorter wavelengths.
•CPA: Chirped pulse amplification. A time-frequency correlation is introduced in a light pulse so that it
may be optically compressed after amplification, greatly increasing the maximum power and decreasing
the minimum pulse length.
•OPA: Optical parametric amplifier. A method of generating continuously variable wavelength laser light
by mixing multiple beams.
W.S. Graves
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High Gain Harmonic Generation
Method to reach short wavelength FEL output from longer
wavelength input seed laser.
Input seed at w0
overlaps electron
beam in energy
modulator undulator.
Modulator is tuned to
w0.
Electron beam
develops energy
modulation at w0.
W.S. Graves
Energy modulation is
converted to spatial
bunching in chicane
magnets.
3rd harmonic
bunching is
optimized in
chicane.
Electron beam radiates
coherently at w3 in long
radiator undulator.
Radiator is tuned to w3.
5
Cascaded HGHG
Output at 3w0
Output at 9w0
Final output
seeds 2nd stage
seeds 3rd stage
at 27w0
Input
seed w0
1st stage
2nd stage
3rd stage
•Number of stages and harmonic of each to be optimized during study.
•Factor of 10 – 30 in wavelength is reasonable without additional
acceleration between stages.
•Seed longer wavelength (100 – 10 nm) beamlines with ~200 nm harmonic
from synchronized Ti:Sapp laser.
•Seed shorter wavelength (10 – 0.3 nm) beamlines with HHG pulses.
W.S. Graves
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Master oscillator
Seed
laser
UV Hall
Fiber link synchronization
Pump
laser
Seed
laser
X-ray Hall
Pump
laser
Undulators
100 nm
Injector
laser
30 nm
Undulators
1 nm
10 nm
0.3 nm
SC Linac
1 GeV
2 GeV
4 GeV
10 nm
3 nm
1 nm
Undulators
Seed
laser
W.S. Graves
Nanometer Hall
Pump
laser
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UV Hall
to master oscillator for timing sync
Single HGHG undulator section
Ti:Sapp + BBO = 200 nm seed
Tune wavelength by OPA
GW power, .01 – 10 ps FWHM
100 nm
Seed
lasers
~10 m length
10 GW peak
Pump
lasers
30 nm
Ti:Sapp + BBO = 200 nm seed
Ti:Sapp + HHG = 10-30 nm seed
Tune by OPA or harmonic number
Direct seeded or cascaded
HGHG undulators
10 nm
~20 m length
10 GW peak
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Nanometer Hall
to master oscillator for timing sync
Direct seeded or cascaded
HGHG undulators
10 nm
Ti:Sapp + BBO = 200 nm seed
Ti:Sapp + HHG = 10-30 nm seed
Tune by OPA or harmonic number
Seed
lasers
~20 m length
10 GW peak
Pump
lasers
Cascaded HGHG undulators
3 nm
Cascaded HGHG undulators
Ti:Sapp + HHG = 10-30 nm seed
Tune by OPA or harmonic number
1 nm
~30 m length
4 GW peak
W.S. Graves
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X-ray Hall
to master oscillator for timing sync
Cascaded HGHG undulators
1 nm
Seed
lasers
Ti:Sapp + HHG = 10-30 nm seed
Tune by OPA or harmonic number
~30 m length
6 GW peak
Pump
lasers
Cascaded HGHG undulators
0.6 nm
Cascaded HGHG undulators
0.3 nm
~60 m length
4 GW peak
(also 0.1 nm at 1% of 0.3 nm intensity)
W.S. Graves
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High-Harmonic Generation
Noble Gas Jet (He, Ne, Ar, Kr)
100 mJ - 1 mJ
XUV @ 3 – 30 nm
@ 800 nm
h = 10-8 - 10-5
t
Propagation
Recombination
0
tb
x
Ionization
Energy
-Wb
wXUV
Laser electric field
W.S. Graves
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High Harmonic Generation Layout
Courtesy of M. Murnane and H. Kapteyn, JILA
W.S. Graves
W.S. Graves, MIT Bates Laboratory
12
HHG enhancements
Pulse shaping of drive
Quasi-phase matching
laser can enhance a
in modulated hollow-
single harmonic line.
core waveguide.
Courtesy of M. Murnane and H. Kapteyn, JILA
How much improvement do we get with additional phase
control for the very high harmonics in the water window
< 4nm ?
W.S. Graves
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HHG enhancements
•HHG has produced wavelengths
from 50 nm to few angstroms, but
power is very low for wavelengths
shorter than ~10 nm.
•Best power at 30 nm.
•Improvements likely to yield 10 nJ
HHG spectra for 3 different
periodicities of modulated
at 5 nm.
•Rapidly developing technology.
waveguides.
Courtesy of M. Murnane and H. Kapteyn, JILA
W.S. Graves
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Initial GINGER simulations at 0.3 nm
What is included
•Fully time dependent…includes short pulse effects.
•Accurately models interaction of seed power with electron beam.
•Includes all electron beam effects: energy spread, time structure,
beam size and divergence.
What is not yet included
•Modeling of HGHG process from long wavelength seed to short
wavelength output.
•Cascaded HGHG sections.
W.S. Graves
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SASE properties
Time profile
Time profile (log plot)
10
10
8
500
8
5
4
3
2
Power (kW/bin)
10
6
Power (W)
Power (GW)
7
6
10
4
10
400
300
200
2
10
100
1
0
Spectrum
0
0
10
20
30
Time (fs)
40
50
10
0
10
20
30
Time (fs)
40
50
0
0.2995
0.3
0.3005
Wavelength (nm)
0.301
GINGER simulation of SASE FEL at 0.3 nm.
Energy
Electron beam parameters
4.0 GeV
Peak current (amp)
RMS emittance
RMS energy spread
2000 A
0.8 mm
.01 %
Charge
80 pC
Beam power
Bunch FWHM
8.0 TW
40 fs
W.S. Graves
Laser beam parameters
Pulse FWHM
35 fs (~ebeam length)
Saturation power
~3.0 GW
Energy
0.2 mJ
FWHM linewidth
7.0E-4
Saturation length
59 m
For simulation speed. True bunch length will be longer.
16
Seeding for short pulse
Output time profile
Time profile (log plot)
10
2
8
1.5
10
1
0.5
1
0
24.5
1000
25
25.5
26
Time (fs)
26.5
Power (kW/bin)
1.5
10
Power (W)
Power (GW)
Power (GW)
2
6
10
4
10
27
2
10
0.5
0
10
20
30
Time (fs)
40
50
GINGER simulation of
seeded FEL at 0.3 nm.
Note: does not include
earlier HGHG stages
800
600
400
200
0
10
0
Spectrum
0
10
20
30
Time (fs)
40
Seed laser parameters
FWHM
Power
Pulse energy
0.5 fs
10.0 MW
5 nJ
50
0
0.2995
0.3
0.3005
Wavelength (nm)
0.301
FEL output parameters
Saturation FWHM
Saturation power
Saturation energy
0.75 fs
~2.0 GW
1.5 mJ
FWHM linewidth
6.0E-4
Undulator length
20 m
Same ebeam parameters as SASE case.
W.S. Graves
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Seeding for narrow linewidth
Output time profile
10
2
10
1.5
10
500
1
0.5
Power (MW/bin)
Power (W)
8
Power (GW)
Spectrum
Time profile (log plot)
6
10
4
10
2
0
0
10
20
30
40
50
Time (fs)
GINGER simulation of
seeded FEL at 0.3 nm.
Note: does not include
earlier HGHG stages
10
300
200
100
10
0
400
0
10
20
30
Time (fs)
40
50
0.3
0.3005
0.301
Wavelength (nm)
Seed laser parameters
FWHM
Power
Pulse energy
0
0.2995
50 fs
0.1 MW
5 nJ
FEL output parameters
Saturation FWHM
Saturation power
Saturation energy
30 fs
~2.0 GW
0.1 mJ
FWHM linewidth
1.0E-5
Saturation length
28 m
Same ebeam parameters as SASE case.
W.S. Graves
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Seeded and SASE comparison
2
2
1.5
1.5
8
1
Power (GW)
Power (GW)
Power (GW)
7
1
0.5
0.5
6
5
4
3
2
1
0
10
20
30
Time (fs)
40
0
50
Power (MW/bin)
Power (kW/bin)
10
20
30
40
50
800
600
400
200
500
500
400
400
300
200
100
0.3
0.3005
Wavelength (nm)
0
Time (fs)
1000
0
0.2995
0
0
Power (kW/bin)
0
0.301
0
0.2995
10
20
30
Time (fs)
40
50
300
200
100
0.3
0.3005
0.301
0
0.2995
Wavelength (nm)
0.3
0.3005
Wavelength (nm)
0.301
Seeded and SASE time profiles and spectra.
Different schemes require different undulator length.
W.S. Graves
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Chirped pulse amplification (CPA)
FEL bandwidth of ~1.0E-3 limits minimum pulse length, while induced
energy spread limits peak power.
These limits can be stretched by overlapping seed pulse that has
time/frequency correlation (chirp) with matching electron beam.
Compress optical beam with grating or crystal following amplification.
energy
frequency
FEL bandwidth
slippage
time
time
Seed optical pulse
W.S. Graves



w
2
Electron pulse
20
Compressed power (W)
Chirped pulse length (s)
CPA FEL speculation
-15
10
-16
10
-17
10
13
10
12
10
11
-9
10
-8
10
Wavelength (m)
-7
10
10
-9
10
-8
10
Wavelength (m)
-7
10
Theoretical pulse length and peak power assuming 50 fs seed pulse
with 6% chirp (3% FWHM ebeam chirp).
Output is sub-femtosecond at TW peak power.
Caveat: compression ratio up to 5000 depends upon no distortion of
optical phase during FEL amplification. (Conventional lasers routinely
exceed 104 compression.)
W.S. Graves
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Femtosecond synchronization
•Goal is to synchronize multiple lasers and electron beam to level of 10 fs.
•MIT has locked multiple independent lasers together with sub-fs accuracy
using an optical heterodyne detector (balanced cross correlator).
•Optical clock community developing fs timing synchronization over longer
distances.
•Our timing requirements are considered quite challenging in the
accelerator community.
W.S. Graves
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Cr:Fo and Ti:Sapp lasers in Kaertner lab
W.S. Graves
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Cross-Correlation Amplitude
Time [fs]
1.0
-100
0
100
Independent Cr:Fo and Ti:Sapp
0.8
lasers synchronized with sub-fs
0.6
timing jitter by F. Kaertner.
Timing jitter 0.30 fs (2.3MHz BW)
0.4
0.2
0.0
0
20
40
Time [s]
60
80
100
Error signal from optical double
balanced mixer.
W.S. Graves
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Source comparison
APS
MIT Bates
Und. A
SASE FEL
Min
bandwidth
seeded FEL
X-rays per pulse
(0.1% max BW)
1.E+08
3.E+11
3.E+11
6.E+09
Peak brilliance
(p/s/0.1%/mm2)
3.E+22
1.E+33
3.E+35
7.E+33
Peak flux (p/s/0.1%)
1.E+18
6.E+24
6.E+24
1.E+23
Avg. flux (p/s/0.1%)
7.E+14
3.E+14
3.E+14
6.E+12
Average brilliance
(p/s/0.1%/mm2)
4.E+19
5.E+22
1.E+25
3.E+23
0.1
4.E+09
3.E+11
6.E+09
73000
50
50
1
Photon beamlines
34
10-30
10-30
10-30
Wavelength (nm)
0.05 - .4
0.3 - 100
0.3 - 100
0.3 - 100
Pulse frequency (Hz)
7.E+06
1000
1000
1000
Degeneracy parameter
Pulse length (fs)
W.S. Graves
Min
pulse length
seeded FEL
25