Post on 13-Jan-2016
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