W.S. Graves

1

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

2

OutlineOutline

•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

3

Seeded beam SASE beam

Output wavelengt

h

FEL param

FEL

tmin (fs) at max

BW

Emin (meV) at 1 ps FWHM

SASE tmin

(fs) SASE Emin

(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

Bandwidth and Pulse LengthBandwidth and Pulse Length

1

2f t

FELff

Seeded beams limited only

by uncertainty principle and

seed properties.

SASE properties determined

by ebeam.

Data from BNL’s

DUV-FEL

experiment

W.S. Graves

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TerminologyTerminology•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 GenerationHigh Gain Harmonic Generation

Modulator is tuned to 0.

Electron beam develops energy modulation at 0.

3rd harmonic bunching is optimized in chicane.

Energy modulation is converted to spatial bunching in chicane magnets.

Input seed at 0

overlaps electron beam in energy modulator undulator.

Electron beam radiates

coherently at 3 in long

radiator undulator.

Radiator is tuned to 3.

Method to reach short wavelength FEL output from longer

wavelength input seed laser.

W.S. Graves

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Cascaded HGHGCascaded HGHG

Input

seed 0

1st stage 2nd stage 3rd stage

Output at 30

seeds 2nd stage

Output at 90

seeds 3rd

stage

Final

output at

270

•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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UV Hall X-ray Hall

Nanometer Hall

4 GeV2 GeV1 GeV

1 nm

0.3 nm

100 nm

30 nm

10 nm

10 nm

3 nm

1 nm

Master oscillator

Pump laser

Pump laser

Seed laser

Seed laser

Seed laser

Pump laser

Fiber link synchronization

Injector laser

Undulators

Undulators

Undulators

SC Linac

W.S. Graves

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to master oscillator for timing sync

Pump lasers

Ti:Sapp + BBO = 200 nm seed Tune wavelength by OPA GW power, .01 – 10 ps FWHM

Ti:Sapp + BBO = 200 nm seed Ti:Sapp + HHG = 10-30 nm seed Tune by OPA or harmonic number

100 nm

30 nm

10 nm

Single HGHG undulator section

Direct seeded or cascaded HGHG undulators

1 G

eV e

beam

UV HallUV Hall

Seed lasers

~10 m length 10 GW peak

~20 m length 10 GW peak

W.S. Graves

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to master oscillator for timing sync

Pump lasersTi:Sapp + BBO = 200 nm seed

Ti:Sapp + HHG = 10-30 nm seed Tune by OPA or harmonic number

10 nm

3 nm

1 nm

Direct seeded or cascaded HGHG undulators

2 G

eV e

beam

Nanometer HallNanometer Hall

Seed lasers

Ti:Sapp + HHG = 10-30 nm seed Tune by OPA or harmonic number

Cascaded HGHG undulators

Cascaded HGHG undulators

~20 m length 10 GW peak

~30 m length 4 GW peak

W.S. Graves

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to master oscillator for timing sync

Pump lasers

1 nm

0.6 nm

0.3 nm

4 G

eV e

beam

X-ray HallX-ray Hall

Seed lasers

Ti:Sapp + HHG = 10-30 nm seed Tune by OPA or harmonic number

Cascaded HGHG undulators

Cascaded HGHG undulators

Cascaded HGHG undulators

~30 m length 6 GW peak

~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 GenerationHigh-Harmonic Generation

Noble Gas Jet (He, Ne, Ar, Kr)

100 J - 1 mJ

@ 800 nm

XUV @ 3 – 30 nm

= 10-8 - 10-5

Recombination

Propagation

-Wb

XUV

En

erg

y

x

b

0

Laser electric field

Ionization

W.S. Graves

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High Harmonic Generation LayoutHigh Harmonic Generation Layout

Courtesy of M. Murnane and H. Kapteyn, JILA

W.S. Graves, MIT Bates Laboratory

W.S. Graves

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Pulse shaping of

drive laser can

enhance a single

harmonic line. Courtesy of M. Murnane and H. Kapteyn, JILA

Quasi-phase

matching in

modulated hollow-

core waveguide.

HHG enhancementsHHG enhancements

How much improvement do we get with additional phase How much improvement do we get with additional phase control for the very high harmonics in the water window control for the very high harmonics in the water window

< 4nm ?< 4nm ?

W.S. Graves

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HHG spectra for 3 different

periodicities of modulated

waveguides.Courtesy of M. Murnane and H. Kapteyn, JILA

•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 at 5 nm.

•Rapidly developing technology.

HHG enhancementsHHG enhancements

W.S. Graves

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Initial GINGER simulations at 0.3 nmInitial 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 propertiesSASE properties

0.2995 0.3 0.3005 0.3010

100

200

300

400

500

Wavelength (nm)

Pow

er (

kW/b

in)

0.2995 0.3 0.3005 0.3010

100

200

300

400

500

Wavelength (nm)

Pow

er (

kW/b

in)

0 10 20 30 40 500

1

2

3

4

5

6

7

8

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 500

1

2

3

4

5

6

7

8

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 5010

0

102

104

106

108

1010

Time (fs)

Pow

er (

W)

0 10 20 30 40 5010

0

102

104

106

108

1010

Time (fs)

Pow

er (

W)

GINGER simulation of SASE FEL at 0.3 nm.

Time profile Time profile (log plot) Spectrum

Electron beam parameters

Energy 4.0 GeV

Peak current (amp) 2000 A

RMS emittance 0.8 m

RMS energy spread .01 %

Charge 80 pC

Beam power 8.0 TW

Bunch FWHM 40 fs

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.

W.S. Graves

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Seeding for short pulseSeeding for short pulse

0.2995 0.3 0.3005 0.3010

200

400

600

800

1000

Wavelength (nm)

Pow

er (

kW/b

in)

0.2995 0.3 0.3005 0.3010

200

400

600

800

1000

Wavelength (nm)

Pow

er (

kW/b

in)

Output time

profile

Time profile (log

plot)

Spectrum

0 10 20 30 40 5010

0

102

104

106

108

1010

Time (fs)P

ower

(W

)0 10 20 30 40 50

100

102

104

106

108

1010

Time (fs)P

ower

(W

)

Seed laser parameters

FWHM 0.5 fs

Power 10.0 MW

Pulse energy 5 nJ

FEL output parameters

Saturation FWHM 0.75 fs

Saturation power ~2.0 GW

Saturation energy 1.5 J

FWHM linewidth 6.0E-4

Undulator length 20 m

0 10 20 30 40 500

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 500

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

24.5 25 25.5 26 26.5 270

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

24.5 25 25.5 26 26.5 270

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

GINGER simulation of

seeded FEL at 0.3 nm.

Note: does not include

earlier HGHG stages

Same ebeam parameters as SASE

case.

W.S. Graves

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Seeding for narrow linewidthSeeding for narrow linewidth

Output time

profile

Time profile (log plot) Spectrum

Seed laser parameters

FWHM 50 fs

Power 0.1 MW

Pulse energy 5 nJ

FEL output parameters

Saturation FWHM 30 fs

Saturation power ~2.0 GW

Saturation energy 0.1 mJ

FWHM linewidth 1.0E-5

Saturation length 28 m

GINGER simulation of

seeded FEL at 0.3 nm.

Note: does not include

earlier HGHG stages

Same ebeam parameters as SASE

case.

0.2995 0.3 0.3005 0.3010

100

200

300

400

500

Wavelength (nm)

Pow

er (

MW

/bin

)

0.2995 0.3 0.3005 0.3010

100

200

300

400

500

Wavelength (nm)

Pow

er (

MW

/bin

)

0 10 20 30 40 500

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 500

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 5010

0

102

104

106

108

1010

Time (fs)

Pow

er (

W)

0 10 20 30 40 5010

0

102

104

106

108

1010

Time (fs)

Pow

er (

W)

W.S. Graves

19

0 10 20 30 40 500

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 500

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 500

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 500

0.5

1

1.5

2

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 500

1

2

3

4

5

6

7

8

Time (fs)

Pow

er (

GW

)

0 10 20 30 40 500

1

2

3

4

5

6

7

8

Time (fs)

Pow

er (

GW

)

0.2995 0.3 0.3005 0.3010

200

400

600

800

1000

Wavelength (nm)

Pow

er (

kW/b

in)

0.2995 0.3 0.3005 0.3010

200

400

600

800

1000

Wavelength (nm)

Pow

er (

kW/b

in)

0.2995 0.3 0.3005 0.3010

100

200

300

400

500

Wavelength (nm)

Pow

er (

MW

/bin

)

0.2995 0.3 0.3005 0.3010

100

200

300

400

500

Wavelength (nm)

Pow

er (

MW

/bin

)

0.2995 0.3 0.3005 0.3010

100

200

300

400

500

Wavelength (nm)

Pow

er (

kW/b

in)

0.2995 0.3 0.3005 0.3010

100

200

300

400

500

Wavelength (nm)

Pow

er (

kW/b

in)

Seeded and SASE comparisonSeeded and SASE comparison

Seeded and SASE time profiles and spectra.

Different schemes require different undulator

length.

W.S. Graves

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Chirped pulse amplification (CPA)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.

time

frequency

FEL bandwidth

slippage

2w

time

energy

Seed optical pulse Electron pulse

W.S. Graves

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10-9

10-8

10-710

11

1012

1013

Wavelength (m)

Com

pres

sed

pow

er (

W)

10-9

10-8

10-710

11

1012

1013

Wavelength (m)

Com

pres

sed

pow

er (

W)

10-9

10-8

10-7

10-17

10-16

10-15

Wavelength (m)

Chi

rped

pul

se le

ngth

(s)

10-9

10-8

10-7

10-17

10-16

10-15

Wavelength (m)

Chi

rped

pul

se le

ngth

(s)

10-9

10-8

10-710

11

1012

1013

Wavelength (m)

Com

pres

sed

pow

er (

W)

10-9

10-8

10-710

11

1012

1013

Wavelength (m)

Com

pres

sed

pow

er (

W)

10-9

10-8

10-7

10-17

10-16

10-15

Wavelength (m)

Chi

rped

pul

se le

ngth

(s)

10-9

10-8

10-7

10-17

10-16

10-15

Wavelength (m)

Chi

rped

pul

se le

ngth

(s)

CPA FEL speculationCPA FEL speculation

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 synchronizationFemtosecond 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

23

Cr:Fo and Ti:Sapp lasers in Kaertner labCr:Fo and Ti:Sapp lasers in Kaertner lab

W.S. Graves

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1.0

0.8

0.6

0.4

0.2

0.0Cro

ss-C

orre

lati

on A

mpl

itud

e

-100 0 100

Time [fs]

100806040200Time [s]

Timing jitter 0.30 fs (2.3MHz BW)

Independent Cr:Fo and Ti:Sapp

lasers synchronized with sub-fs

timing jitter by F. Kaertner.

Error signal from optical double

balanced mixer.

W.S. Graves

25

Source comparisonSource comparisonAPS MIT Bates

Und. ASASE FEL

Min bandwidth

seeded FEL

Min pulse length 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

Degeneracy parameter

0.1 4.E+09 3.E+11 6.E+09

Pulse length (fs) 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