Generation of Ultrafast Mid-IR pulses using a 100 MeV ERL-FEL

(Drivers for tunable HHG based coherent X-Ray sources ?)

T. Popmintchev, nature photonics | VOL 4 | DECEMBER 2010

Phase matched HHG using mid-IR lasers (Experiments)

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: ~100m-200m )

Generation of coherent X-Ray pulses by HHG

OPCPA’s

•NIR sub-10 fs with 70 J energy at 100kHz.

• NIR sub-10 fs multi-kHz, multi-mJ

•Mid-IR (~3m) sub-100 fs with a few micro-Joule energy at 100kHz

•3.9 m sub-100 fs with 6 mJ at 10-20Hz

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 mid-IR (and beyond 10 m 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)

• 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 ~22 m) (single spike, high gain superradiant FEL osc.)

Generation of short electron pulses (JLab)

Ultrashort Pulse Generation in (Mid IR) FELs

E ~ 60 MeV (NIR/MIR)E ~ 13 MeV (FIR)135 pC pulsesz ~ 0.5 – 4 ps10.7 MHz (21.4 MHz FIR)

Parameter NIR FEL MIR FEL FIR FELWavelength (μm) 2.5 to 27 8 to >150 100 to 1100Wawenum (cm−1) 400 to 4000 < 70 to 1300 9 to 100

FSU-NHMFL NIR/MIR/FIR (&broadband THz) FEL Proposal

X

MIR/FIR

FIR

NIR

inclusion of a HHG based coherent X-Ray source ?

Beam parameters FEL (~3-6m) Units

Beam Energy 100 MeV Bunch charge 80 pC _z rms bunch length 0.1 ps norm.Trans. Emittance 5 mm.mrad

_e rms energy spread 0.5% Beam pulse rate 40 (?) MHz Macropulse form 100s (?) Average current 0.30 - 1.9(?) mA

Wiggler parameters

Type planar

Wiggler period 60 mm

Wiggler Krms 1.7-2.6

Periods 25 (30)

Trim Quads reading

Beam parameters FEL (1.6m) Units

Beam Energy 115 MeV

Bunch charge 110 (135) pC

_z rms 150 fs

Peak current ~300 A

_e rms(uncorrelated)

0.1%

_e rms (correlated)

0.5%

nor. trans. Emit. 8 rad

rep. rate ~75 MHz

Coherent OTR interferometer autocorrelationscans for bunch length measurements

system parametersBERLinPro JLab IR FEL

stretcher

compressor

PLE

dielectric mirrorNIR/MIR FELO

mode matching telescope

- Beam Energy: 100 MeV

- Bunch Charge: 80 pC

- Rep rate: 40 MHz

- Outcpl.Pls. Energy: 50-70J

- Cav. Enhancement: 80-100

-Pulse width: ~100-200fs (fwhm)

-IL ~ 1x1014 – 3.5x1014W/cm2

- 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-lockedNIR Laser

- Depending on the recombination time of the fast switch, sequence of micropulses with several ns separation can be ejected from the EC !

Suggested (3-6m) MIR FEL & Pulse Stacker Cavity

Brewster W.

vacuum vessel

Opt. Switch mount

Folded cavity

FEL

Input Coupler

High Reflector

T. Smith @ Stanford IR-FEL achieved enhancement of ~70 - 80 using an external pls stacker cavity (1996)

Q ~ 40 (Finesse ~ 300 ) enhancement :~90

Q~ 50enhancement :~130-140

estimated enhancement @ JLab ~ 100

Enhancement Cavity @ JLab

5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2

0.0

0.2

0.4

0.6

0.8

1.0

200th pass after Saturation

wavelength [m]

no

rm. S

pe

ctra

l In

ten

sity

-200 0 200 400 600 800 1000 1200-5.0x108

0.0

5.0x108

1.0x109

1.5x109

2.0x109

2.5x109

3.0x109

3.5x109

Intracavity Power (overlap over 200 pulses after Saturation)

time [fs]

Po

we

r [W

atts

]

2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6

0.0

0.2

0.4

0.6

0.8

1.0

200th pass after Saturation

no

rm.

Sp

ect

ral I

nte

nsi

ty

wavelength [m]

0 200 400 600 800

0

1x109

2x109

3x109

4x109

5x109

6x109 Intracavity Power (overlap over 200 pulses after Saturation)

Po

we

r [W

atts

]

time [fs]

~ 3 m

/~ 4%-5%

100fs (fwhm)

200fs (fwhm)

3 m - 6 m Short Pulse FEL (cavity detuning)

/~ 4%-5%

- low time jitter

- low peak to peak power deviations

- Outcoupled Pulse Enegies: ~ 50-70 J

~ 10 cycle pulses (HHG drive laser)

~ 6 m

Talk in Nov. 2010

150 200 250 300 350 400 450 500 550

0.0

5.0x1010

1.0x1011

1.5x1011

2.0x1011

Intracavity power level in superradiance mode

P

ow

er

[Wa

tts]

time [fs]

High Gain (superradiant) FEL Oscillator operating at cavity synchronization

rs ESynchrotron Osc. Freq.

• nearly an order of magnitude higher outcoupled pulse intensity (despite low outcoupling ratios)

• FEL efficiency in superradiance mode more than doubled

2.5 3.0 3.5 4.0 4.5 5.0

0.0

0.2

0.4

0.6

0.8

1.0

chirped pulse spectrum in superradiance mode

wavelength [m]

no

rm. S

pe

ctra

l In

ten

sity

0 1000 2000 3000 4000

0.000

0.002

0.004

0.006

0.008

0.010Intracavity pulse energy in superradiance mode

Pu

lse

En

erg

y [J

]

roundtrip #

35 - 40fs (fwhm)

lc ~ 45fs

Talk in Nov. 2010

Comparison between two FEL simulation methods

3 4 5 6 7 8

0.0

2.0x102

4.0x102

6.0x102

8.0x102

1.0x103

1.2x103

1.4x103

1.6x103

1.8x103

spec

tral

inte

nsity

[a.

u.]

wavelength [m]

3.1m 6.2m

3 4 5 6 7 8 9 10

0.0

2.0x103

4.0x103

6.0x103

8.0x103

1.0x104

1.2x104

1.4x104

spec

tral

inte

nsity

[a.

u.]

wavelength [m]

3.1m 6.2m

3D (semi-)frequency domain

3 4 5 6 7 8 9

0.0

2.0x1012

4.0x1012

6.0x1012

8.0x1012

1.0x1013

1.2x1013

1.4x1013

1.6x1013

1.8x1013

spec

tral

inte

nsity

[a.

u.]

wavelength [m]

3.1m 6.2m

1½D - SVEA time domain

(superradiant) FEL Oscillator@ synchr.' case ‘FEL oscillator-cav. detuning' case

good agreement between the models in 'FEL oscillator with cavity detuning' case

(in terms of outcoupled pulse energy, temporal and spectral pulse profiles)

Disagreements in the 'superradiant operation at cavity synchronism' in obtaining self similar pulses following saturation, differences in temporal and spectral pulse profiles.

: timing jitterL : cavity lengthL: cavity length detuningf : bunch rep. frequency (perfectly synchronized to L) : cavity roundtrip time ( 2L/c)

/ = L/L + f/f

e- bunch

FEL Osc. sensitivity to temporal jitter

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.

~ 6 m

• Peak power fluctuations ~4-5% rms

• Pulse width fluctuations limited to a few %

• timing jitter ~ ±20 fs (optical pulse)

0 100 200 300 400 500 600 700 800

0.0

5.0x108

1.0x109

1.5x109

2.0x109

2.5x109

3.0x109

time [fs]

Pow

er

[Wa

tts]

Jitter 5 fs rms

0 100 200 300 400 500 600 700 800

0.0

5.0x108

1.0x109

1.5x109

2.0x109

2.5x109

3.0x109

3.5x109

time [fs]

Po

wer

[W

att

s]

Jitter 10 fs rms

0 100 200 300 400 500 600 700 800

0.0

5.0x108

1.0x109

1.5x109

2.0x109

2.5x109

3.0x109

time [fs]

Po

we

r [W

att

s]

w/o initial Jitter

FEL Osc. sensitivity to temporal jitter ~ 6 m

Simulation using BERLinPro parameters, 'FEL oscillator with cavity detuning'

0 100 200 300 400 500 600

0

1x109

2x109

3x109

4x109

5x109

time [fs]

Po

we

r [W

att

s]

P~2% rms

100fs (fwhm)

• Pulse width fluctuations limited to a few % rms

• Timing jitter ~ ±20 fs (optical pulse)

~ 3 m

• Peak power fluctuations ~8 -10% rms

0 100 200 300 400 500 600

0

1x109

2x109

3x109

4x109

5x109

6x109

time [fs]

Po

we

r [W

att

s]

jitter 5 fs rms w/o initial jitter

FEL Osc. sensitivity to temporal jitter

Simulation using BERLinPro parameters, 'FEL oscillator with cavity detuning'

Timing jitter measurements @ JLab IR-FEL

• 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 m ) on arrival time jitter : L/L < 3.8x10-8

( 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)

FEL Osc. sensitivity to temporal jitter ~ 6 m

jitter 2.5 fs rms

w/o initial jitter

jitter 2.5 fs rms

0 100 200 300 400 500 600

0

1x1010

2x1010

3x1010

4x1010

5x1010

6x1010

7x1010

8x1010

9x1010

time [fs]

Pow

er [W

atts

]

0 100 200 300 400 500 600-1x1010

0

1x1010

2x1010

3x1010

4x1010

5x1010

6x1010

7x1010

time [fs]

Po

we

r [W

atts

]

0 100 200 300 400 500 600

0

1x1010

2x1010

3x1010

4x1010

5x1010

6x1010

7x1010

time [fs]

0 100 200 300 400 500 600

0

1x1010

2x1010

3x1010

4x1010

5x1010

6x1010

7x1010

time [fs]

Pow

er [W

atts

]

0 100 200 300 400 500 600

0

1x1010

2x1010

3x1010

4x1010

5x1010

6x1010

7x1010

time [fs]

jitter 2.5 fs rms

jitter 2.5 fs rms

1D-SVEA Simulation using BERLinPro parameters, 'superradiant operation at cavity synchronism'

-0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.060

0.005

0.01

0.015

0.02

0.025

~5E

r

-0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0

0.005

0.01

0.015

0.02

0.025

~E

r

• 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 %)

Calculated spent beam energy distribution @FEL saturation

=3 m

=6 m