Generation of Ultrafast Mid-IR pulses using a 100 MeV
ERL-FEL
(Drivers for tunable HHG based coherent X-Ray
sources ?)
Generation of coherent X-Ray pulses by HHG
 Idea (A.Foehlisch): Can we drive HHG by a compact
ERL(FEL)?
 requirements imposed on drive lasers :
- HHG (phase matched) needs preferably few cycle to ~10 cycle drive
laser pulses in NIR/MIR and intensities in the range of 1-5x1014 W/cm2
(noble gas filled hollow waveguide apertures: ~100mm-200mm )
Phase matched HHG using mid-IR lasers (Experiments)
OPCPA’s
•NIR sub-10 fs with 70 mJ energy at
100kHz.
• NIR sub-10 fs multi-kHz, multi-mJ
•Mid-IR (~3mm) sub-100 fs with a few
micro-Joule energy at 100kHz
•3.9 mm sub-100 fs with 6 mJ at 10-20Hz
T. Popmintchev, nature photonics | VOL 4 | DECEMBER 2010
Outline :
 short term: carrying out the HHG experiments on an
existing FEL facility that meets the requirements set on the
mid-IR drive laser, verifying the theory throughout the midIR (and beyond 10 mm if necessary) (JLab ???)
 long term: mid-IR ERL-FELs should be able to perform
better than atomic lasers in terms of :
 tunability (throughout the nir/mid IR and beyond)
- rep rate (MHz) in generating mJ(s) of ultrafast pulses with
high average power (problems in CEP stabilization???)
simulation study has been and still is mainly focused on the
latter and on the question:
What system requirements will be imposed on a compact
ERL, (particularly concerning timing jitter budget)
Ultrashort Pulse Generation in (Mid IR) FELs
• Chirped pulse generation in a FEL oscillator using a
chirped electron beam and pulse compression (JLab)
• Mode-locking techniques in FELs
-Active mode-locking (multiple OK sections used in a
cavity)
 - Passive mode-locking (JAERI, lasing at l~22 mm)
(single spike, high gain superradiant FEL osc.)
 Generation of short electron pulses (JLab)
FSU-NHMFL NIR/MIR/FIR (&broadband THz) FEL Proposal
E ~ 60 MeV (NIR/MIR)
E ~ 13 MeV (FIR)
135 pC pulses
sz ~ 0.5 – 4 ps
10.7 MHz (21.4 MHz FIR)
X
FIR
NIR
inclusion of a HHG based
coherent X-Ray source ?
MIR/FIR
Parameter
Wavelength (μm)
Wawenum (cm−1)
NIR FEL
2.5 to 27
400 to 4000
MIR FEL
8 to >150
< 70 to 1300
FIR FEL
100 to 1100
9 to 100
system parameters
BERLinPro
Beam parameters
Beam Energy
Bunch charge
s_z rms bunch length
norm.Trans. Emittance
s_e rms energy spread
Beam pulse rate
Macropulse form
Average current
FEL (~3-6mm)
100
80
0.1
5
0.5%
40 (?)
100ms (?)
0.30 - 1.9(?)
Units
MeV
pC
ps
mm.mrad
MHz
mA
JLab IR FEL
Beam parameters
FEL (1.6mm)
Units
Beam Energy
115
MeV
Bunch charge
110 (135)
pC
s_z rms
150
fs
Peak current
~300
A
s_e rms
0.1%
s_e rms
0.5%
(uncorrelated)
(correlated)
nor. trans. Emit.
rep. rate
8
mrad
~75
MHz
Wiggler parameters
Type
Wiggler period
Wiggler Krms
Periods
planar
60
1.7-2.6
25 (30)
mm
Trim Quads reading
Coherent OTR interferometer autocorrelation
scans for bunch length measurements
Suggested (3-6mm) MIR FEL & Pulse Stacker Cavity
- Beam Energy: 100 MeV
- Bunch Charge: 80 pC
compressor
- Rep rate: 40 MHz
- Outcpl.Pls. Energy: 50-70mJ
- Cav. Enhancement: 80-100
-Pulse width: ~100-200fs (fwhm)
-IL ~ 1x1014 – 3.5x1014W/cm2
stretcher
mode matching
telescope
- high-Q enhancement cavity
(EC) smoothes out power and
timing jitter of the injected pulses
inherent to FEL interaction.
- allows fs (10 -100 ?) level
synchronization of the cavity
dumped mid-IR pulse with the
mode-locked switch laser.
Mode-locked
NIR Laser
PLE
dielectric mirror
NIR/MIR FELO
- Depending on the recombination time of the fast switch, sequence of
micropulses with several ns separation can be ejected from the EC !
Enhancement Cavity @ JLab
Folded cavity
Input
Coupler
vacuum
vessel
FEL
Q ~ 40 (Finesse ~ 300 )
enhancement :~90
Q~ 50
enhancement :~130-140
estimated enhancement
@ JLab ~ 100
High
Reflector
Brewster W.
Opt. Switch
mount
T. Smith @ Stanford IR-FEL achieved enhancement of ~70 - 80
using an external pls stacker cavity (1996)
3 mm - 6 mm Short Pulse FEL (cavity detuning)
~ 3 mm
6 x1 0
5 x1 0
9
200
In tra ca vity P o w e r (o ve rla p o ve r 2 0 0 p u lse s a fte r S a tu ra tio n )
100fs (fwhm)
9
th
p a ss a fte r S a tu ra tio n
1 .0
Dw/w~ 4%-5%
0 .8
3 x1 0
2 x1 0
1 x1 0
9
n o rm . S p e ctra l In te n sity
P o w e r [W a tts ]
4 x1 0
9
9
9
0 .6
0 .4
- low time jitter
0 .2
- low peak to peak
power deviations
0 .0
0
0
200
400
600
2 .9
800
3 .0
3 .1
~ 6 mm
200
In tra ca vity P o w e r (o ve rla p o ve r 2 0 0 p u lse s a fte r S a tu ra tio n )
3 .5 x1 0
3 .0 x1 0
3 .2
3 .3
th
3 .5
- Outcoupled Pulse
Enegies: ~ 50-70 mJ
3 .6
p a ss a fte r S a tu ra tio n
9
Dw/w~ 4%-5%
1 .0
200fs (fwhm)
9
3 .4
w a ve le n g th [ m m ]
tim e [fs]
0 .8
2 .0 x1 0
1 .5 x1 0
1 .0 x1 0
5 .0 x1 0
9
n o rm . S p e c tra l In te n s ity
P o w e r [W a tts]
2 .5 x1 0
9
9
9
8
0 .6
0 .4
0 .2
0 .0
0 .0
-5 .0 x1 0
8
-2 0 0
0
200
400
600
tim e [fs]
800
1000
1200
5 .6
5 .8
6 .0
6 .2
6 .4
6 .6
w a ve le n g th [ m m ]
6 .8
7 .0
7 .2
~ 10 cycle pulses
(HHG drive laser)
High Gain (superradiant) FEL Oscillator operating at cavity synchronization
In tra ca vity p o w e r le ve l in su p e rra d ia n ce m o d e
Synchrotron Osc. Freq.
Er
P o w e r [W a tts ]
s 
1 .5 x1 0
1 .0 x1 0
5 .0 x1 0
11
1 .0
35 - 40fs (fwhm)
11
n o rm . S p e c tra l In te n s ity
2 .0 x1 0
ch irp e d p u lse sp e ctru m in su p e rra d ia n ce m o d e
lc ~ 45fs
11
10
0 .8
0 .6
0 .4
0 .2
0 .0
0 .0
150
200
250
300
350
400
450
500
550
2 .5
3 .0
tim e [fs]
3 .5
4 .0
4 .5
5 .0
w a ve le n g th [ m m ]
In tra ca vity p u lse e n e rg y in su p e rra d ia n ce m o d e
0 .0 1 0
• FEL efficiency in superradiance mode more
than doubled
0 .0 0 8
P u lse E n e rg y [J]
• nearly an order of magnitude higher
outcoupled pulse intensity (despite low
outcoupling ratios)
0 .0 0 6
0 .0 0 4
0 .0 0 2
0 .0 0 0
0
1000
2000
ro u n d trip #
3000
4000
Comparison between two FEL simulation methods
(superradiant) FEL Oscillator@ synchr.' case
‘FEL oscillator-cav. detuning' case
3D (semi-)frequency domain
1 .2 x1 0
1 .0 x1 0
8 .0 x1 0
6 .0 x1 0
4 .0 x1 0
2 .0 x1 0
1 .8 x1 0
3 .1 m m
6 .2 m m
4
4
3
3
3
sp e ctra l in te n sity [a . u .]
1 .2 x1 0
1 .0 x1 0
8 .0 x1 0
6 .0 x1 0
4 .0 x1 0
2 .0 x1 0
1 .0 x1 0
8 .0 x1 0
6 .0 x1 0
4 .0 x1 0
3 .1 m m
6 .2 m m
3
3
3
3
2
2
2
2
0 .0
4
5
6
7
8
9
10
3
4
5
6
7
8
w a ve le n g th [ m m ]
w a ve le n g th [ m m ]
1 .4 x1 0
1 .2 x1 0
2 .0 x1 0
3
1 .6 x1 0
1 .4 x1 0
3
3
0 .0
1 .8 x1 0
1 .6 x1 0
sp e ctra l in te n sity [a . u .]
sp e ctra l in te n sity [a . u .]
1 .4 x1 0
4
1½D - SVEA time domain
13
13
3 .1 m m
6 .2 m m
13
13
 good agreement between the models in
'FEL oscillator with cavity detuning' case
(in terms of outcoupled pulse energy,
temporal and spectral pulse profiles)
13
12
 Disagreements in the 'superradiant
operation at cavity synchronism' in
obtaining self similar pulses following
saturation, differences in temporal and
spectral pulse profiles.
12
12
12
0 .0
3
4
5
6
7
w a ve le n g th [ m m ]
8
9
FEL Osc. sensitivity to temporal jitter
Dt/t = dL/L + df/f
e- bunch
Dt : timing jitter
L : cavity length
dL: cavity length detuning
f : bunch rep. frequency (perfectly synchronized to L)
t : cavity roundtrip time ( 2L/c)
 Bunch time arrival variation effectively has the same effect
as cavity length detuning.
 effect of the timing jitter on the FEL performance
In slippage dominated short pulse FEL oscillators cavity
detuning is necessary to optimize the temporal overlap
between optical and e- pulses (Lethargy effect).Timing jitter
induces fluctuations on the operational cavity detuning.
FEL Osc. sensitivity to temporal jitter
~ 6 mm
Simulation using BERLinPro parameters, 'FEL oscillator with cavity detuning'
3 .0 x1 0
P o w e r [W a tts]
2 .5 x1 0
2 .0 x1 0
1 .5 x1 0
1 .0 x1 0
9
Jitter 5 fs rms
2 .5 x1 0
9
9
9
2 .0 x1 0
1 .5 x1 0
1 .0 x1 0
5 .0 x1 0
5 .0 x1 0
w/o initial Jitter
9
9
P o w e r [W a tts ]
3 .0 x1 0
9
9
9
9
8
8
0 .0
0 .0
0
100
200
300
400
500
600
700
800
tim e [fs ]
3 .5 x1 0
3 .0 x1 0
P o w e r [W a tts]
2 .5 x1 0
2 .0 x1 0
1 .5 x1 0
1 .0 x1 0
5 .0 x1 0
100
200
300
400
500
600
700
800
tim e [fs ]
• Peak power fluctuations
~4-5% rms
9
Jitter 10 fs rms
9
0
9
• Pulse width fluctuations
limited to a few %
9
9
9
• timing jitter ~ ±20 fs
(optical pulse)
8
0 .0
0
100
200
300
400
tim e [fs ]
500
600
700
800
FEL Osc. sensitivity to temporal jitter
l~ 3 mm
Simulation using BERLinPro parameters, 'FEL oscillator with cavity detuning'
5 x1 0
P o w e r [W a tts ]
4 x1 0
3 x1 0
2 x1 0
1 x1 0
9
5 x1 0
9
w/o initial jitter
jitter 5 fs rms
9
4 x1 0
DP~2% rms
9
9
P o w e r [W a tts]
6 x1 0
9
9
3 x1 0
2 x1 0
1 x1 0
9
9
100fs (fwhm)
9
9
0
0
0
100
200
300
400
500
600
tim e [fs ]
0
100
200
300
400
500
600
tim e [fs]
• Peak power fluctuations
~8 -10% rms
• Pulse width fluctuations
limited to a few % rms
• Timing jitter ~ ±20 fs (optical pulse)
Timing jitter measurements @ JLab IR-FEL
( P. Evtushenko , ELECTRON BEAM TIMING JITTER AND ENERGY MODULATION MEASUREMENTS AT THE JLAB ERL )
(Beam Current Monitor (cavities) and Signal Source Analyzer employed for power
spectrum measurements at harmonics to characterize phase noise)
• phase noise spectra measured in the vicinity of the
wiggler-entrance (behind the bunch compressor)
• e- bunch length: 150 fs rms
• average current : 0.5 mA to 4.5 mA (bunch charge ~135
pC kept constant, bunch rep rate varied)
• measured timing jitter :
~25 fs rms @ 1.5 mA - ~80 fs rms @ 4.5 mA
• estimated FEL spec (to keep pp-power fluct. below 10 %
@ l = 1.6 mm ) on arrival time jitter : dL/L < 3.8x10-8
FEL Osc. sensitivity to temporal jitter
~ 6 mm
1D-SVEA Simulation using BERLinPro parameters, 'superradiant operation at cavity synchronism'
P o w e r [W a tts ]
6 x1 0
5 x1 0
4 x1 0
3 x1 0
2 x1 0
1 x1 0
10
7 x1 0
10
jitter 2.5 fs rms
10
9 x1 0
6 x1 0
10
5 x1 0
10
4 x1 0
10
3 x1 0
10
2 x1 0
10
1 x1 0
10
8 x1 0
7 x1 0
10
P o w e r [W a tts]
7 x1 0
10
10
10
6 x1 0
5 x1 0
4 x1 0
3 x1 0
2 x1 0
10
1 x1 0
0
0
0
100
200
300
400
500
600
0
100
6 x1 0
P o w e r [W a tts]
5 x1 0
4 x1 0
3 x1 0
2 x1 0
7 x1 0
10
6 x1 0
10
5 x1 0
10
4 x1 0
300
400
500
600
10
10
3 x1 0
jitter 2.5 fs rms
10
10
10
10
10
10
1 x1 0
10
0
0
-1 x1 0
10
0
100
200
300
tim e [fs]
400
500
600
w/o initial jitter
10
10
10
10
10
10
10
0
100
200
300
tim e [fs ]
0
100
200
300
tim e [fs]
10
2 x1 0
1 x1 0
200
tim e [fs]
10
10
0
tim e [fs ]
7 x1 0
10
400
500
600
400
500
600
Calculated spent beam energy distribution @FEL saturation
• 8% -10% spent beam momentum spread (full)
generated by the FEL interaction
• large energy spread acceptance is required
for beam transport/energy recovery
(JLab IR Upgrade acceptance :~15 %)
0.025
0.02
0.025
~5sE
l=3 mm
0.02
0.015
DN/N
DN/N
0.015
0.01
0.005
0
-0.08
~5sE
l=6 mm
0.01
0.005
-0.06
-0.04
-0.02
Dg/gr
0
0.02
0.04
0.06
0
-0.08
-0.06
-0.04
-0.02
Dg/gr
0
0.02
0.04
0.06