M. Zepf-Ultrafast X-Ray and Ion Sources From Multi-PW Lasers
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Transcript of M. Zepf-Ultrafast X-Ray and Ion Sources From Multi-PW Lasers
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Ultrafast X-ray and Ion
sources
from multi-PW lasers
Matt Zepf
Queen’s University Belfast
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Outline
• Ion Acceleration via Radiation Pressure Acceleration
– GeV/u
– Narrow energy distributions
– Attosecond ion bunches
– First demonstration of ‘Light-sail’ regime
• Relativistically Oscillating Mirrors (HHG from Solid Targets)
– Relativistically oscillating mirrors
– Attosecond and zeptosecond pulses
– Extreme brightness with ELI conditions
• Relativistic Mirrors
– Light Sail Regime (thin target)
– Holeboring regime (Semi-infinite target)
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I>1019Wcm2
a0>3
Relatvistic electron production
Hot electron propagation
MeV energy, µC charge
Space charge field:
E~Thot/ Debye~MeV/µm=1012V/m
MeV/u protons and ions
Typical targets: Metallic foils
Proton Source: CH Contamination on foil surfaces (typically ~50Å)
THE TNSA Mechanism
(Target Normal Sheath Accleleration))
Target
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Typical results
106
107
108
109
1010
1011
Pro
tons/
MeV
40353025201510
Proton Kinetic Energy (MeV)
15 J 42 J 110 J
• Target: 10µm Al
• Temperature
~ 1.8 MeV for 12 J
~ 5 MeV for 85J
• Energy conversion
~2 10-3 for 12 J
~5 10-2 for 85 J
~1 10-1 for 400 J
• Efficiency at 30-35 MeV
hot~10-5-10-4
10 MeV 22 MeV17 MeV
Typical divergence:
30-60°
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Beam quality
nm scale surface perturbations are still visible
- irreducible emittance of <0.004 mm mrad
From Cowan et al, PRL 2004
µm scale
virtual source
30-60° divergence
x ~10-3mm x 1 rad ~ 1 mm mrad
Excellent probe for
fields in plasmas
(M. Borghesi et al.)
Plasma
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Laser accelerated protons
- an exciting source for the future
• Unique for short pulse duration
– Unrivalled for time resolved probing
– Excellent emittance
• Compared to conventional acceleratorswhat do we need to be competitive?
– Higher average flux
– Narrow angular distribution
– Narrow energy distribution (not simply slicing)
– Higher endpoint energy• 200 MeV protons required for 200mm range in H2O (e.g.
for hadron therapy)
• Fewer particles at higher repetition rate (e.g. hadron therapy)
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Beam energy scaling – typically ~I1/2
(Robson, et al., Nature Physics (2006)
500fs scaling: 200 MeV protons requires >4 1021Wcm-2 (>1kJ)
Schreiber Scaling: 200 MeV at 100J, 40fs
Efficiency into >200 MeV around 10-5-10-4 !
Can we do better?
Schreiber et al., PRL (2006)
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A novel approach is required -
Radiation Pressure Acceleration (RPA)
Extreme Laser pressure at high intensities:
PL=2I/c=6 Gbar @ 1019Wcm-2
Velocity estimated by momentum conserv.
(accelerated mass balances laser momentum)
niMivi2= vi
2=I/c
vi=(I/ c)1/2
Ei~IRadiation Pressure Accelearation scales faster
than TNSAWilks et al (PRL 92)
Zepf et al., Phys. Plasmas (1996)
30fs
60fs
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Relativisitic equations of motion for whole foil acceleration: LIGHT SAIL REGIMEL
~I/ niMiL
Radiation Pressure Acceleration- using circular polarisation (e.g. Robinson, Zepf et al, New J. Phys, 2008)
Ch
arge d
ensity
x
~ I/
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At I>1023 Wcm-2RPA dominates over TNSA:
GeV protons with quasi-monoenergetic
distribution for Elaser=10kJ(Simulations by Esirkepov et al., PRL 175003 (2004))
Far beyond ELI first stage…
In the limit of thin foils, extreme intensity: Ep~ GeV
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Intermediate intensity - RPA and TNSA coexist
TNSA~I1/2
At 5 1020 Wcm-2 acceleration
due to radiation pressure
becomes comparable to TNSA.
Can we exploit the faster
Emax I scaling?
L.O. Silva et al. PRL 92, 015002 (2004)
RPA
Problem: TNSA decompresses foil during RPA
=> Foil becomes transparent!
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Radiation Pressure Acceleration-circular polarisation suppresses TNSA
For I=1021 Wcm2
Circular polarisation suppresses hot electron generation - no TNSA, few -rays
RPA dominates for realistic intensities.
102
100
101
x[µm]
0 5 10
40
20
0
y[µ
m]
200 600 1000 200 600 1000Energy [MeV] Energy [MeV]
Pro
ton
Nu
mb
er (
a.u
.) 105
104
103
102 Pro
ton
Nu
mb
er (
a.u
.) 105
104
103
102
x[µm]80 120 160
x[µm]80 120 160
1.5
1
0.5
-0.5
0
1.5
1
0.5
-0.5
0
106
105
102
101
104
103
px/m
pc
Px/m
pc
RPA – Circ Pol TNSA- Linear
(Robinson et al, NJP 2008)
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Foil thickness:100nm150nm
250nm350nm
RPA scaling - a promising route
Time (fs)
0 100 200 300 400 400
500
400
Pro
ton
en
ergy [
MeV
]
300
200
100
0
Co
nversio
n E
fficie
ncy
1
.8
.6
.4
.2
200 MeV predicted in quasi-monoenergetic beam at ~ 1021 Wcm-2
Feasible ELI specfication laser at high repetition rate
Efficiency into 200 MeV peak >60%
Divergence angle: 4°
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Quasi-monoenergetic proton beams from RPA
- first experimental demonstration
Data from LIBRA
consortium taken on
Astra GEMINI
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Transition to the light-sail regime
I=4 1020Wcm-2
I=9 1020Wcm-2
Ep~I1.75
Ep~I0.8
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Light Sail: acceleration to GeV/uat ELI parameters
Stable acceleration to GeV energies shown for I=2…6 10 22 Wcm-2
(Simulations: B. Qiao et al, PRL 2009)
Control of laser or target radial distribution essential for ultimate performance
Solid density bunch
Duration:100nm/c= 0.3 fs
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bea
m
dir
ecti
o
n
Fs
cat
Fg
rad
Hi-Rep strategy for complex targets
Wafer target production
Electrostatic Injection
Optical trapping
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RPA light sail – the story so far.• RPAwith circular polarisation.
• Low divergence
• High efficiency
• Quasi-Monoenergetic distribution
• Little other radiation (gammas, fast electrons)
• Unique features• Extremly short bunches – attosecond duration
• Solid density bunches (quasi-neutral)
• Synchronisation to optical sources at attosecond level possibl
• Challenges• Maintaining 1D nature during acceleration.
• High repetition, high power lasers to drive accelerator
• GeV accelerator simulation E=0.5- 2kJ, 30 fs
• 200 MeV: E~100J, 60 fs,
Ultrafast probing
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Ultrabright laser driven attosecond sources
1) Relativistically Oscillating
Mirrors
Extreme Intensities
Coherent Harmonic Focusing
Attosecond Bunching
Tests of QED using the Relativistically Oscillating Mirror
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Relativistically Oscillating Plasma Surfaces
as non-linear medium
Electron kinetic energy = rest mass for a0=(I 2/1.37 1018Wcm-2)1/2=1
Highly relativistic for a0>>1 ( ~a0)
Relativistically Oscillating Surface
Courtesy of G. Tsakiris, MPQ
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fout
f in
1 v /c
1 v /c~ 4 2 tout
tin~
1
4 2
Shorter Pulses - Higher Frequencies
The relativistic Doppler effect
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=33
ELI laser can generate Relativistic Mirrors
=10fs, =800nm
=2.5as, =2Å,
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Plasma
Laser Driven Oscillation
X(t)
Rest
Position
vs
c
t´
Upshifting from an oscillating surface
γs
t´
At these times high harmonics are generated!
s
1
1 vs c2
~T0/ max
1)Upshifting is restricted to a short time ~T0/ max.
2)The upshifted pulse has a duration of O~ / ~ T0/
From Fourier theory, the spectrum must extend to frequencies O~
Predicted pulse duration ~10-19s=100zeptoseconds for =20
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A sufficiently intense laser can be used to move electrons in a
target at relativistic velocities.
A sharp edged plasma will act as an oscillating, relativistic mirror.
with = [1+a02/2]1/2
10-30 is possible with latest lasers
Gordienko et al. PRL 93, 115001, 2004
Orders > 1000,
keV harmonics!
asymptotic efficiency ~n-8/3for >>1
Harmonics up to nmax~81/2
Independent of intensity!
Dromey et al., Nature Physics, (2006.)
Experimental data
From Vulcan PW
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• Boost due to
– Increased focusability
– Attosecond pulse duration
Enhancement up to the Schwinger limit theoretically possible(Gordienko et al. PRL,94, 103903 (2004)
HHG BOOSTS theoretically achievable intensity.
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• How realistic is this in the real world?
– No phase distortions on target.
– No scattering of higher harmonic due to surface
roughness.
Ideal world: focal spot size reduced by n2
FLAT SURFACE
Diffraction limited n= Laser/n
At a0>>1
Laser
Target
PARABOLIC SURFACE
Divergence: =f/D
Diffraction limited focus ~f n/D
Reflected Laser
Focusing
Harmonic
Target Laser
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Dynamic effects: Ponderomotive Denting
0 10 20 30x (c/ 0)
0
10
20
30
y (
c/
0)
100 fs
PLASMAVacuum
Laser
Ponderomotive denting due to Gbar
light pressure
f
DHARMONIC
BEAM
Harmonics emitted into constant angle even for initially flat targets
n=Max( Laser/n, f/D)
(from Wilks et al. PRL 1992)
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Experimental Results
Wavelength (nm)
An
gle
(m
rad
)
ROM orders
CWE orders
Diffraction limit
I=2 1019Wcm-2
p=50fs
From: Dromey, Zepf, Nature Physics, 5, 146, 2009
500fs, 1020 Wcm-2
50fs, 1019 Wcm-2
Divergence vs harmonic order
Experimental dent vs PIC
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GAUSSIAN FOCUS
SUPERGAUSSIAN
WAVEFRONT CONTROL
Preshaped targets (laser machining in situ?)
Pulse duration (5fs -> 2mrad divergence in above expt.)
Intensity distribution (supergaussian)
Divergence and focus control
From Hörlein et al,
EPJ D 55, 475–481 (2009)
Simulations by S. Rykovanov
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• Changing roughness does not affect specular reflection –
data consisten with denting only
• Specular reflection observed for initial roughness > n
Is target roughness a limiting factor ?
- diffuse or specular reflection for high orders
Dromey et al, PRL 99, 085001 (2007)
keV harmonics are beamed
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• Initial roughness of target is smoothed out
– Simulations by Sergey Rykovanov.
• Focusing to extreme intensities appears feasible
Relativistic plasma dynamics smooth initial roughness
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0.01
0.1
1
10
100
1000
10 100 1000 10000
Puls
e d
ura
tio
n (
as
)
nF
Duration of attosecond pulses
n=(21/p-1)nF
Few as pulses
possible <1keV
Zeptosecond@
>1keV
nF
Extremely short pulses are possible
Harmonic efficiency slope as n-p
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Harmonics 10 -14 (CWE)
XUV pulse train with ~0.9 fs duration
(in collaboration with MPQ at ATLAS)
Y. Nomura et al., Nature Physics 2009
Attosecond pulse measurement
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• Pulse duration reduces
with n:
~n-1
• Diffraction limited
focus:
w0~n-2
Peak intensity of attosecond pulses
• Single harmonic
efficiency:
~n-8/3
• Pulse efficiency (for ~n
harmonics forming the
as pulse)
~n-5/3
34
21
35
max nnn
n
A
EIIntensity increases:
Opens up new regime of high intensity X-ray science
Tool for probing vacuum physics
Coherent superposition of entire spectrum ICHF=a03 I0
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Probing vacuum bi-refringence
X-ray
probe
2d
probe
n4
15
d
probe
I
IcritPhase Shift:
Probe wavelength as short as possible (polarised X-ray)
Intensity as high as possible, long interaction length
2
2
2
ellipticity:
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• Requires bright polarised X-ray probe
• Requires time synchronisation << laser
• Requires ultra-intense laser >>1024 Wcm-2
• Requires excellent polariser
Practical experiments are challenging
X-ray
probe
Ultraintense laser
(e.g. ELI
Polariser
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Reflected Laser
Focusing
Harmonic
Target Laser
Relativistic Mirrors for experimental QED?
-Boosted intensity by CHF
-Harmonics are intrinsic probe of CHF
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I[Wcm-2] Length 2
1µm 1022 20 3.8 10-10 1.5 10-19
1nm 1022 20 3.8 10-7 1.5 10-13
1Å 1024 20 0.002 1 10-6
1Å 1026 2 0.02 1 10-4
What magnitude do we expect?
X
X
• Intensity boost via CHF and synchronised short
wavelength probe makes observation feasible
(measurement limit of 2 to date ~ 10-6)
• How well polarised are the harmonics (the high
power laser?)
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Summary
• Extreme Intensities beyond current limit
– Coherent Harmonic Focusing
– Attosecond bunching
• Ultrabright attosecond source
• Well suited to tests of QED
• Extreme X-ray physics
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Ultrabright laser driven attosecond sources
2) Relativistic Flying Mirrors
Extreme Intensities
Coherent Harmonic Focusing
Attosecond Bunching
Tests of QED using the Relativistically Oscillating Mirror
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Relativistic Flying Mirror
Reflectivity:For =const expect upshift of r/ i=4 z
2; NOTE: 4 z2~2 <<4
Coherent reflection: L< (ki z2)-1
Bulanov S V et al PRL 2003; B. Qiao et al, NJP 2009
z
Blowout condition:
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a0=60, n/nc=200, z~7; max~100
PIC confirms upshift + Reflectivity (B. Qiao et al.,NJP 2009)
z2~213
Chirp produces broad spectrum
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A bright, monochromatic future?
Laser vg=c~vfoil => interaction time >> laser
= (t) => Strong chirp in upshift
Possible solution: secondary foil to reflect drive laser and transmit
Relativistic Mirror
=const => monochromatic upshift
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Wu+Meyer-ter-Vehn:
2nd foil enables z= max
(arXiv:1003.1739)
Ultrabright narrowband sources
at 100s of keV are possible
Towards bright coherent -rays
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SUMMARY.
• ELI Beamlines facility is ideall placed to exploit emerging laser driven sources
• Radiation Pressure Ion sources
• Ultrashort bunches
• Compact accelarators to GeV/u level
• Science and Medical applications
• Relatvistic mirror sources
• Ultrabright attosecond sources
• Extreme X-ray Intensities possible (extreme source brightness with ELI)
• Towards zeptosecond regime
• Narrowband X-ray and Possibly -ray with Relativistic Flying Mirror
Ultrafast probing
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Light-Sail and Holeboring regime
Holeboring Regime
a~I/
Ch
arge d
ensity
x
Light Sail Regime
a~I/
Holeboring acceleration takes place in thick target limit
=> more relaxed requirements
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Acceleration depends on local intensity for sufficiently short pulses!
Ultra-short pulses (here 4 cycles) reduce energy requirements.
Gaussian foci acceptable (reduced energy requirements)
From Macchi et al. PRL 2005
Acceleration Propagation phase
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Dimensionless holeboring parameter:
Target:
~0.2
Holeboring – I/ scaling
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0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
1020 1021 1022 1023 1024
70.8 kgm^(-3)30 kgm^(-3)1000 kgm^(-3)
Intensity (Wcm-2)
Low density targets are desirable
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Liquid H2, 30 fs pulse
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Liquid H2, 30 fs pulse.
Spectral control possible by tailoring pulse shape/density profile: I/ =const.
1021Wcm-2 6×1021Wcm-2
6×1022Wcm-21022Wcm-2
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Existing Hydrogen Jets are suitable for Holeboring
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Holeboring acceleration.• Desirable features.
• High efficiency
• Quasi-Monoenergetic distribution possible
• Little other radiation (gammas, fast electrons)
• Semi-infinite targets
• Gaussian foci (no 1D requirement)
• Suitable for current high repetition rate technology• For I=6 1022 Wcm-2: E= 5J, 1µm focus, 10fs
=> These are PFS parameters to a achieve 400 MeV/u
• Challenges• Maintaining 1D nature during acceleration.
• High repetition, high power lasers to drive accelerator
• GeV accelerator simulation E=0.5- 2kJ, 30 fs
• 200 MeV: E~100J, 60 fs,
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Summary - Protons
• Laser accelerated protons (TNSA)– Excellent beam emittance
– Unique beam characteristics – excellent short pulse ion source
– ps temporal resolution of electric field evolution
– But:Slow scaling to high beam energies, broad spectrum
• RPA schemes
– Highly desirable beam qualities with circular polarisation.• Low divergence
• High efficiency
• Quasi-Monoenergetic distribution
• Little other radiation (gammas, fast electrons)
– Potentially ideal for medical applications.
– Excellent laser beam control is essential for light sail
– Relaxed operating conditions for holeboring regime
• High repetition, high energy beams appear within reach.
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Plasma Mirror
- an ultra-fast optical switch
A low reflectivity surface (i.e. a piece of glass with AR coating can operate as
~100fs rise time optical switch:
- Illuminate with Imax> plasma formation threshold
- prepulse sees Rcold<10-2
-main pulse sees Rplasma~60-80%
- contrast enhancement: Rplasma/Rcold~ 100
Disadvantages: Energy loss, new PM required every shot.
A
A
A
Plasma
Mirror
Advantage: Interaction with near-perfect plasmas surfaces is possible.
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Experimental set-up
15Mev
0
5
10
15
20
25
30
35
40
0 500 1000 1500 2000 2500
5Mev 10Mev
Detector depth [µm]
Proton energy loss
En
erg
y lo
ss [K
eV
/µm
]
0
5
10
15
20
25
30
35
0 5 10 15 20 25
layer Alayer B
RCF layer number
Pro
ton
en
erg
y [M
eV
]
Layered detector stacks give 2D energy resolved beam images
Detector Stack
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Quasi-monoenergetic proton beams from RPA
- first experimental demonstration
0
2 1012
4 1012
6 1012
8 1012
1 1013
4 8 12 16 20
Pro
ton
s/M
eV
/sr
Energy [MeV]
-1 1013
0
1 1013
2 1013
3 1013
4 1013
5 1013
6 1013
7 1013
0 5 10 15 20 25
Pro
ton
s/M
eV
/sr
Energy [MeV]
Astra Gemini results
LIBRA consortium
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Beam quality - spectral
1ps
E
t 100ps
E
t200ps
Typical conventional accelerator @20MeV E/E=10-4 :
E t~2keV*10ns=20 10-6 eV s
Laser accelerator: E t~10 MeV*1ps=10 10-6 eV s
Comparable to conventional accelerator
After phasespace rotator
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Circular polarisation
- suppression of foil heating and expansion
Copious hot electrons
TNSA
Gamma ray production
No hot electrons
Suppressed TNSA (foil expansion)
Fewer gamma rays
Simulations by Sergey Rykovanov, MPQ (published
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Reflected waveform contains attosecond bursts of harmonics every at
every -spike
t
a)
Laserf
IFT
c)
f
I
d)
FT
t
I
e)
t
E
b)
E
t
Many cycle interaction
Attosecond pulse generation
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For a few cycle pulse the highest harmonics are only generate in one cycle
-> isolated attosecond pulse
t
IFT
e)
t
a)
f
I
d)
f
IFT
c)
E
t
t
E
b)
Few cycle interaction
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Attosecond pulses by spectral filtering
Removing optical harmonics + fundamental changes wave
from from saw-tooth to individual as-pulses
from (G. D. Tsakiris et al.,New J. Phys. 8, 19(2006)
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0
0.2
0.4
0.6
0.8
1
-15 -10 -5 0 5 10 15
CircularLinear
|E|
Time [fs]
Electric field does not oscillate for circular polarisation –
light pressure becomes quasi-static
P~I/c~E2/c