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QED IN ULTRA-INTENSE LASER
FIELDS
TOM HEINZL
PIF2010, KEK, TSUKUBA
24 NOVEMBER 2010
With: N. Iji, K. Langfeld (UoP), C. Harvey, A. Ilderton, M. Marklund (Ume), A. Wipf (Jena),H. Schwoerer (Stellenbosch), B. Kmpfer, R. Sauerbrey, D. Seipt (FZD)
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Outline
1. Introduction
2. Strong Fields: Theory
3. rong e s: xamp es1. Nonlinear Compton Scattering
2. Laser Pair Production
3. Vacuum Birefringence4. Conclusion and Outlook
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Introduction
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50 Years of Laser Development
Important parameter:
dim.less amplitude
Energy gain of
across laser wavelength
: relativistic
(adapted from Mourou, Tajima, Bulanov, RMP 78, 2006)
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Regime of Extremes Current magnitudes:
Power
Largest e.m. fields currently available in lab
But: fields pulsedand alternating
Electric field
Magnetic field
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Laser Projects CLF Vulcan 10 PW
1023 Wcm-2
Construction by 2014 (?)
Bud et: 20 M ?
ELI
>100 PW (Exawatt ?)
>1025 Wcm-2
Budget: several 100 M
Construction by 2016 (?)
Building (projected)
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2. Strong Fields: Theory
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Modelling a laser In order of increasing complexity:
Plane wave Infinite (IPW)
Pulsed (PPW)
w
z0
Finite T-duration Infinite transverse extension
Gaussian beam:
Finite transverse waist w
Finite longitudinal extensionz0
T
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Plane waves: peculiarities Null wave vector
Electromagnetic field only dependent on invariant phase
Null:
No intrinsic invariant scale!
Need (probe) momentum to build invariants
E.g. (TH, A. Ilderton, Opt. Comm. 2009)
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Charge in IPW Solution of Lorentz force eq.: rapid quiver motion
(momentum ) Charge acquires quasi-momentum
Longitudinal addition consequence:
Effective mass squared
The basic intensity effect!
(Sengupta 1951, Kibble 1964)
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Strong-field QED Probe photons
Volkov soln of Dirac eqn in PWfield (Volkov 1935)
ec rons resse y aser p o ons---------
Volkov electron:
Build transition amps between Volkov electrons from
Feynman rules (`Furry picture)
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Main issues
Intensity dependence of elementary processes
see below
Finite (beam) size effects (see below )
Beyond plane waves (? )
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Exploring intensity dependence High intensity ( ) = uncharted region of
standard modelenergy
Hi h-intensit QED
all-optical
Backscattered
(5 GeV )
100 102 103 106
1Vulcan
1PW
10PW
ELISLAC
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3.1 Nonlinear Compton Scattering (NLC)3. Strong Fields: Examples
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NLC scattering Expand Furry picture Feynman diagram
Sum over all processes of the type
Schott 1912; Nikishov/Ritus 1964,
Brown/Kibble 1964, Goldman 1964
emission
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NLC: main features No energy threshold!
Classical limit: Thomson ( ) For : frequency upshift
Used for
X-ray generation
Nonlinearity:
Terawatt laser pulse(a0 = 0.05)
Electron Bunch
(e = 235)
Femtosecondgamma-ray pulse
(0.78 MeV)
T-REX, LLNL (2008)
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NLC cont
d
For high intensity,
modified Compton edge
In particular:
Higher harmonics: n >1 (nonlinear)
Overall blueshift maintained as long as Redshift of n=1 edge
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NLC spectrum: maina0 effects
Linear Compton
edge
Higher
harmonics, n >1
Red-shift
C. Harvey, TH, A. Ilderton,
PRA 79, 2009
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a0 dependence (lab)
Tuning a0similar to changing frame: when
inverse Compton Compton C. Harvey, TH, A. Ilderton, PRA 79, 2009
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Finite Size Effects
Strongly focussed: Weakly focussed:
laser
ee
laser
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Finite Size NL Thomson Spectra
Strongly focussed: Weakly focussed:
= 0 mrad
= 5 mrad
= 10 mrad
TH, D. Seipt, B. Kmpfer, PRA 81, 2010
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3.2 Laser Pair Production (PP)3. Strong Fields: Examples
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Stimulated PP
Obtained from NLC via crossing
Main new feature: energy threshold
Experiment SLAC E-144 (1995): combine bothprocesses ...
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SLAC E-144 (Bula et al. 96, Burke et al. 97)
Two stages: NLC
stimulated PP
New development: prediction of pair cascades(Bell, Kirk et al.; Narozhny, Fedotov, Ruhl et al.)
Gil Eisner, Photonics Spectra 1997
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Stimulated PP: finite-size effects
IPW:
triple-diff rate = deltacomb
above threshold ( )
PPW: dependence on cycles
per pulse,
Sub-threshold signals
IPW approached for
TH, A. Ilderton, M. Marklund, 2010
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Wave train vs. pulse: vs.
Spectrum = fingerprint of pulse!
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Spontaneous (vacuum) PP (G. Dunnes talk)
Feynman diagram
vacvacuum
breakdown
Im = 0~
Nonzero for , (Schwinger 1951)
Identically zero for pure (no work done)
Identically zero for PW ( compensates )
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3.3 Vacuum Birefringence (VB)3. Strong Fields: Examples
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Heisenberg, Euler 1936
...even in situations where the [photon] energy is
not sufficient for matter production, its virtual
possibility will result in a polarization of thevacuum and hence in an alteration of Maxwells
equations.
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Optical Theorem (Kramers-Kronig)
Total PP rate can be obtained via
Virtual dipoles feel presence of
Re : change of polarisation state diagonalisation of (for X-fields = PW )
two nontrivial eigenvalues
Vacuum polarisation
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Vacuum birefringence (Brezin, Itzykson 1970)
Calcite crystal
wo n ces o re rac on (Toll 1952)
Dim.less (small) parameters:
Field strength:
Probe frequency
fine structure const
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Experiment: measure ellipticity
Phase retardation of e+
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Analysis
ellipticity (squared)
ower aw suppresse
Optimal scenario @ ELI
large intensity:
large probe frequency (X-ray, ):
New record in polarisation purity: @ 6 keV(Marx et al., Opt. Comm., 2010)
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for : 3 GeV @ ELI, 10 GeV @ Vulcan10PW
Large-birefringence via NLC
(Toll 1952
TH, O. Schrder
NB: SLAC E-144 had
Shore 2007)
(K. Langfeld)
Anomalous dispersion Absorption PP
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Summary
Stimulated PP
vacuum PP
NL Compton/Thomson
Vacuum birefringence
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Conclusion
Laser power approaching exawatt regime
Extreme field physics Schwinger limit: QED Experiments planned or under way
-ray genera on:
Theory ( dependence) :
Ok for plane wave models
Challenge: incorporate realistic laser beam model Finite size effects
Beyond plane waves
Numerical approaches
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for your attention
Thank you very much...