High harmonics from gas, a suitable source for seeding FEL  

from vacuum-ultraviolet to soft X-ray region (XUV)

http://loa.ensta.fr/ UMR 7639

G. LAMBERTguillaume.lambert@ensta.fr

Palaiseau - FRANCE

22/08/11

http://loa.ensta.fr/ UMR 7639

Laserlab Integrated Infrastructures Initiative RII-CT-2003-506350 TUIXS European project (Table top Ultra Intense XUV Sources)

FP6 NEST-Adventure n.012843 European Research Council Paris ERC project 226424

M.E. Couprie, M. Labat, O. Chubar Synchrotron Soleil, Gif-sur-Yvette, France

D. Garzella, B. Carré CEA, DSM/SPAM, Gif-sur-Yvette, France

T. Hara, H. Kitamura, T. Shintake, Y. Tanaka, T. Tanikawa SPring-8/RIKEN Harima Institute, Hyogo, Japan

B. Vodungbo, J. Gautier, A. Sardinha, F. Tissandier, Ph. Zeitoun, S. Sebban, V. Malka LOA ENSTA-Paristech, Palaiseau, France

J. Luning LCPMR, Paris

C.P. Hauri Paul Scherrer Institute, Villigen, Switzerland

M. Fajardo Centro de Física dos Plasmas, Lisboa, Portugal

Thanks to JSPS

XUV Free Electron Lasers (FEL) : SASE

1

FLASH (2004, down to 4.1 nm), SCSS (2007, 50 nm), SPARC (2009, 160 nm)…

SASE: Self Amplified Spontaneous Emission

-High number of photon : 1012 photons -Short pulse duration (sub ps)

peak power (GW)-Relatively high repetition rate (tens Hz)-High wavelength tuning-Variable polarization-Good wavefront (Bachelard, PRL 106, 2011)

-Good spatial coherence (Ischebeck, NIMA 507, 2003)

very performing tool for user experiment but…

λ, t

Accelerator

SASE limitations

2

1

Wavelength (nm)

0.8

0.6

0.4

0.2

0

Inte

nsity

(ar

b. u

nit.)

165164163162161160159158157

-Weak gain at short wavelength, single passlong undulator (tens m)

-Relatively important shot to shot variations: intensity, temporal/spectral profilejitter for pump-probe experimentslimited temporal coherence (Saldin, Opt. Commun. 202, 2002)

λ, t

-Coherent

Improvement of the temporal coherence

-Intense

Decreasing of the saturation length

=> shorter undulator

How to reduce/supress SASE limitations: “seeding fully coherent light” in XUV ?

3

Accelerator

SASE

Seeded

About the same gain

XUV radiation : Harmonics produced from gas (HHG)

λ, tExternal source

Previous demonstrations in IR with CO2 and Ti: Sa lasers, then in UV with crystals(Yu, Science 289, 2000)

Why proposing High Harmonics Generated in gas (HHG) ?

4

Rare gas

Laser

Lens

~1014 W/cm2

Odd harmonics

Harmonic order

Num

ber

of p

hoto

n

Cut-off

● Spatially and temporally coherent

● Relatively tunable

● Short pulse duration (10-100 fs)

● Conversion efficiency (10-5 to 10-7)

~ 100 nJ - nJ

-Limited energy per pulse Compared to SASE shot noise?

-Regular and quasi-perfect Gaussian shape

-Spectral width / ~5

-Pulse duration / ~20Unseeded: 1 ps

HHG: 50 fsSeeded: 50 fs

Strong improvement of the temporal coherence/SASE

-High amplification

Direct seeding with HHG at 160 nm at SCSS: fundamental spectrum

SCSS Test Accelerator (Japan) at 150 MeV with 4.5 m long undulator sections

Wavelength (nm)

1

0.8

0.6

0.4

0.2

0

Inte

nsity

(A

rb.

Un.

)

165164163162161160159158157

SASE x 13.7

HHG x 9270

Seeded

2 μJ (40 MW)

5

(Lambert, Nature Physics 4, 2008)

Intense and coherent emission at short wavelength while E=150 MeV 6

81.58180.58079.5

Unseeded

Seeded: 3 nJ (50 kW)

Inte

nsity

(ar

b. u

n.)

1

0.8

0.6

0.4

0.2

0

Wavelength (nm)54.253.853.453

Unseeded x 125

Inte

nsity

(ar

b. u

n.)

1

0.8

0.6

0.4

0.2

0

Seeded: 4 nJ (75 kW)

-Odd and even harmonics from 2nd (80 nm) to

7th (23 nm)

-Clear amplification

-Regular and quasi Gaussian spectral shape

-Spectral narrowing

-Shorter pulse duration

Improvement of the temporal coherence

Wavelength (nm)

302622 24 28 32

Unseeded

H5

H6H7

Inte

nsity

(ar

b. u

n.)

1

0.8

0.6

0.4

0.2

0

Wavelength (nm)

H2 H3

Non Linear Harmonic spectra

(Tanikawa, EPL 94, 2011)

Seeded: 55 pJ (1 kW)

Evaluation of the seed level requirement for observing coherent emission

For Eseed≥88 pJ:

-Stable emission -Regular and quasi Gaussian spectral profiles

Seeding in XUV !

Wavelength (nm)162161160 164163159

0.8

0.6

0.4

0.2

0.0

1.0

Nor

mal

ized

inte

nsity

(a

rb. u

n.)

Ver

tical

pos

ition

(m

m)

EFEL=12.2 nJEseed=88 pJ

HHG

Eseed=0 pJ

Eseed=88 pJ

Eseed=14 pJ

Eseed=14 pJ EFEL=1.4 nJ

Eseed=0 pJ EFEL=0.87 nJ

HHG seed Eseed=88 pJ

3

2

1

0

3

2

103

2

10

3

2

10

Ver

t. po

s. (

mm

) 88 pJ (160 nm) ―> 10 pJ (spatial overlapping) or ~ 200xPe, shot noise

At 13 nm (Pe, shot noise <10 W) ―>

Eseed < 0.7 nJ (200x10Wx10x35fs)

8

Very weak level of injection

Below 13 nm is a challenge!

(Lambert, EPL 88, 2009)

Name Wavelength (nm) state Seeding process Country

SCSS Test Accelerator

60 / 160 demonstrated Direct HHG Japan

SPARC 160 / 266 demonstrated Direct HHG / HGHG Italy

sFlash 38-13 Due 2010-2011 Direct HHG Germany

Fermi 100-10 Due 2011-2012 HGHG, direct HHG? Italy

SwissFEL 5 Due 2018 EEHG, direct HHG Switzerland

SPARX 15 Due ? HGHG, direct HHG? Italy

Overview of the HHG seeded FELs

9

(Giannessi, Proceedings FEL10 JACOW (2011)Labat WE0B3)

(Togashi, Optics Express 19, 2011)

Keep the simplicity of the classical HHG setup

Already obtained

-fs pulse duration

-Full coherence

-High repetition rate: kHz HH currently First MHz HH in xenon (J. Boullet et al. optics letters, 34, 1489 (2009))

To be improved

-Intensity at short wavelengths

-Tuneability (only odd HH):=> need to considerably chirp the driving laser and/or change the gap of the undulator

-Wavefront: diffraction limited beam (aberration-free) => need to drastically clip the IR or HH beam or use adaptive optics for IR or HH

-Variability of the polarization

-Stability of the shot to shot intensity

Harmonics properties relevant for seeding

What has to be improved on HHG for seeding FEL in future?

10

Two colour mixing

Lens

Ti: Sa

ω HarmonicsNoble gas

IR Filter~1014 W/cm2

Technical principle:

BBO crystal

2ω

PPoffCut UIE 2.3

2LaserLaserp IU

ω +2ωX 25Neon

-double harmonic contenteven types:2x(2n+1) from 22x(2n) from the mixing

-increase of the number of photons-redshift:

High order harmonics generated with a two-colour field

(Lambert, NJP 11, 2009)

11

Ar, ω +2ω

He, ω +2ω Ne, ω +2ω

Xe, ω +2ω Ar, ω

He, ω Ne, ω

Xe, ω

100 µm thick BBO crystal, and with the optimization parameters corresponded to ω: Eω<6 mJ, LC=7-9 mm and PG=30-35 mbar

104

103

102

101

100

7570656055504540353025201510

Alcut

Wavelength (nm)

Inte

nsity

(ar

b. u

n.)

(x 100)

(x 25)

(x 0.5) (x 0.5)-Flat spectra (same

intensity level for odd and

even harmonics)

-Increase limited at high

wavelengths due to an

already relatively high

efficiency for Xe and Ar

=> ω+2ω technique

compensates the weak

efficiency at short

wavelengths

Harmonic spectra obtained with either ω or ω+2ω technique

(Lambert, NJP 11, 2009)12

I2ω~1 Iω~0.8

H17H15

H19H21H23

Iω~1.2 I2ω~2.9 Iω~3.9

I2ω~5.4 Iω~4.4

H22

H18

H14

H27H25

Φ=20 mm

/6 rms

0

0.5

1

/5 rms /17 rms

Φ=40 mm

Φ=20 mm

100 m thick BBO crystal

-iris clipping technique:

change the focusing geometry/energy

clean the major part of the distortions in the outer

part of the beam: to /6 rms

-ω (LC=8 mm and PG=30 mbar) to

ω+2ω (LC=4 mm and PG=16 mbar)

-very high increase on 2x(2n+1) type of even

harmonics (50 nJ) due to strong blue/IR and

distortions limited:/5 rms

-iris clipping: limited decrease of intensity

But distortions about /17 rms:

First aberration-free high harmonic beam

Wavelength (nm)60555045403530

Ene

rgy

per

puls

e (n

J)

Iω and I2ω in 1014 W.cm-2 50

40

30

20

10

0

Φ=40 mm

Optimization of both flux and wavefront (Ar gas)

(Lambert, EPL 89, 2010)

13

Already obtained

-fs pulse duration

-Full coherence

-High repetition rate: kHz to MHz soon

-Intensity at short wavelengths

-Tuneability: both odd and even harmonics

Use parametric amplifier (1.2-1.5 m)

-Wavefront: aberration-free beam

-Simple system

To be improved

-Variability of the polarization

-Stability of the shot to shot intensity?

Then next?

15

Circularly polarized HH

-Using circular IR beam

-Two step setup: linear IR beam + polarizer

(Vodungbo, Optics Express 19, 2011)

16

User applications in XUV: SASE-FEL vs HH

In XUV performances are close: weak flux harmonics weak temporal coherence

Single shot coherent diffraction imaging of nano-object (Ravasio et al. PRL 103 (2009)

32 nm, 1μJ, 20 fs

Reconstructed image with 119 nm resolution

17

Pump-probe experiments

Natural synchronization between Laser and HH

Coherent diffraction imaging of magnetic domains (Vodungbo, EPL 94, 2011) :

-Magnetic domain orientation: 45°+- 10°-Width distribution of magnetic domains: 65 nm +- 5 nm

18

q~ λD/aD

1200 s

Co M2,3 edge at 60 eV

Aligned magnetic domains

MFM

a

Ultra-fast demagnetization

-much shorter time scale-better temporal resolution for HH?And/or due to XFEL at 800 eV (L edge)

Integrated density gives magnetization : I ~ M2

(Boeglin, Nature 465, 2010)

19

Thank you for your attention

5

How to perform a HHG seeding experiments ?

Various undulator configurations

e-Electron source

Chicane

Spectrometer device

HHG

Laser

Gas

Refocusing system

1) Generate HHG with as much as possible photons

2) Refocus HHG at the electron beam size inside the undulator for strong interaction

3) Align precisely HHG beam on the undulator axis

4) Tune HHG wavelength with FEL one

5) Synchronize ebeam and HHG below ps time scale

Stabilization of the FEL wavelength

1

0.8

0.6

0.4

0.2

0

Inte

nsi

ty (

arb

. u

n.)

Wavelength (nm)

165164163162161160159158157

Seeded

162.8

162.0

161.2

160.4

159.6

Data file number

2018161412108642

1

0.8

0.6

0.4

0.2

0

Inte

nsity (a

. u.)

Wa

vele

ng

th (

nm

)

~60 s

1009080706050

1

0.8

0.6

0.4

0.2

0

Inte

nsity (a

. u.)

~300 s162.8

162.0

161.2

160.4

159.6

Wa

vele

ng

th (

nm

)

Data file number

1

0.8

0.6

0.4

0.2

0

SASE

7

Stabilization of the FEL wavelength

161.10 nm ± 0.10 nm rms

162.8

162.0

161.2

160.4

159.6

Data file number

2018161412108642

1

0.8

0.6

0.4

0.2

0

Inte

nsity (a

. u.)

Wa

vele

ng

th (

nm

)

~60 s

1009080706050

1

0.8

0.6

0.4

0.2

0

Inte

nsity (a

. u.)

~300 s162.8

162.0

161.2

160.4

159.6

Wa

vele

ng

th (

nm

)

Data file number

+-57%

161.03 nm ± 0.63 nm rms

+-37%

7

-λ stabilized

by a factor of 6

-Still important

intensity variation

(mainly due to

synchronization trouble)

Lens

Ti: Sa

ω HarmonicsNoble gas

IR Filter~1014 W/cm2

Theoretical and technical principles:

BBO crystal

2ω

Semi-classical model in three steps:

PPoffCut UIE 2.3

2LaserLaserp IU

ω +2ωX 25Neon

-double harmonic contenteven types:2x(2n+1) from 22x(2n) from the mixing

-increase of the number of photons-redshift:

High order harmonics generated with a two-colour field

HHG

Ip

xWE=ex.Esint

Tunnel ionizationt~T/4

Radiating recombinationt~T

Initial statet~0

Oscillation in the laser field

t~3T/4

(Lambert, NJP 11, 2009)

11

General set-upSpherical

multilayer mirror

Transmission grating (2000 lines/mm)

CCD Camera

Spectrometer

800 nm 1 kHz< 7 mJ 35 fs

BBO crystal,

(100 m or 250 m thickness)

Gas cell(4 to 7 mm long)

Aluminium filters(200 nm thickness)

Lens, f=1.5 m Calibrated XUV

photodiode

Iris

Grid CCD Camera

Wavefront sensor

Wavefront sensor

y/L

Hole array CCD camera

L

y

Aberrated spot centroid position

Ab

erra

ted

w

avef

ron

t

Reference spot centroid position

Ref

eren

ce f

lat

wav

e fr

ont

2ω

BBO

414.1400800

Waist ratio between ω and 2ω:

iris

Cleaning the distortions with the 2nd harmonic generation

Harmonics from ω+2ω

Gas cell

IR beam wavefront

ω

Filter Wavefront sensor

10.50

A. U.

1.4 time smaller for V and H sizes

From ω From ω+2ω

HH source sizes

3.471.730

A. U.

10.50

A. U.

From ω From ω+2ω

HH footprint sizes

Summary of wavefront optimization

/6 rms /5 rms

/17 rms

ω +2ω, Φ=20 mm

ω +2ω,Φ=40 mmω,Φ=20 mm

-10 -5 0 5 10

10

5

0

-5

-10(4)

RMS (0.100λ), PV (0.483λ)

Horizontal dimension (mm)

Ver

tical

dim

ensi

on (

mm

)

ω, deform. mirror (52 em act.), Ф=15 mm

λ/10 rms

0

0.5

1

λ=32 nm (ω) to 44 nm (ω+2ω)

(b)

(a) BBO crystal(100 μm thickness)

Aluminium filters(200 nm thickness)

SiO2 flat mirror

45° incidenceB4C/Mo/Si flat mirror

λ/2 waveplate

800 nm1 kHz< 7 mJ35 fs

Lens, f=1.5 m

Iris

Transmission grating

(2000 lines/mm)

Spherical multilayer

mirror

CCD Camera

Optical system

Gas cell

ω H

V

H

V

H

V

ω2ω

HHG from ω+2ω

(c)

ω, Hor. Pol.

2n+1

2nΦ2n+1

2ω, Vert. Pol. Φ2n

Time (fs)

-60 -40 -20 20 40 60-80 0

Inte

nsity

(10

14 W

. cm

-2)

0

0.8

1.2

1.6

2

0.4

ω

2ω

-variation of polarization between odd and even harmonics:Higher for longer wavelengths-variation of polarization from one order to another

Aluminium filter

-80 nm-17 nm: intense XUV harmonic

signal

Ar (ω+2ω) intensity increase for 1 over

2 even harmonics

Ne (ω+2ω) intensity about Ar (ω)

intensity (typical reference)

-13 nm: Ne (ω +2ω) about 0.3 nJ

(Lambert, EPL 88, 2009) ~ 200 x PSASE, noise at

13 nm (PSASE, noise ~ 10 W)

=> Eseed ~ 0.7 nJ (200 x 10 W x 35 fs)

-Intensity could have been more optimized

with more energy and longer focusing

Wavelength (nm)

Ar, ω +2ω

Ne, ω +2ω

Ar, ω

Estimation of the Ne spectra content:below 17 nmat 13 nm

Ene

rgy

per

pul

se (

nJ)

100

10

1

0.16055504540353025201510

Alcut

Perspectives of the two-colour HHG for seeding of FEL

-Only relative control on the SHG/HHG◘ I2w/Iw ok ◘ t =18 fs /100 μm not ok◘ Δt2w/Δtw not ok 0

0.5

1

Inte

nsity

(a.

u.)

Time (fs)-60 6030-30 0

ω

2ωΔt2ω

t

14