Diapositive 1

1
High-order harmonics from plasma mirrors basic
mechanisms and properties
F.Quéré SPAM, CEA Saclay, France
Experimental HHG spectrum from plasma mirror
2
High-order harmonics from plasma mirrors basic
mechanisms and properties
C.Thaury, H. George, F.Quéré, M.Bougeard, P.
Monot, Ph. Martin SPAM, CEA Saclay, France
J.P. Geindre, P. Audebert LULI, Ecole
Polytechnique, France
R. Marjoribanks University of Toronto, Physics
Department, Canada
Two PIC codes are used
EUTERPE (1D and boosted frame), developed by
G.Bonnaud (CEA/SPAM) CALDER (1D to 3D), developed
by E. Lefebvre (CEA/DAM)
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HHG from plasma mirrors
Igt few 1015 W/cm2 _at_800 nm
Optically-polished Solid target
l/10
ncme0wL2/e2 nc1.7 1021 cm-3 _at_ 800 nm
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Outline

• 1- Basic mechanismsCoherent Wake Emission
  (CWE)Relativistic Oscillating Mirror (ROM)

2- Experimental evidenceFrom a few 1015 W/cm2 to
1019 W/cm2
3- Phase properties of individual harmonicsROM
? CWE
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Basic mechanisms
What do we learn from PIC simulations ?
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Physics of HHG from plasma mirrors
PIC Simulation- Euterpe code
Density80.nc Short (non-vanishing) density
gradient I6.1017 W/cm2 , P-polarized
F.Quéré et al, Phys. Rev. Lett. 96 (2006)
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Two mechanims are involved
PIC Simulation- Euterpe code
Density80.nc Short (non-vanishing) density
gradient I6.1017 W/cm2 , P-polarized
F.Quéré et al, Phys. Rev. Lett. 96 (2006)
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Two mechanims are involved

• Relativistic Oscillating Mirror
• Doppler effect

Bulanov et al, Phys. Plasmas 1 (1994)
Lichters et al, Phys. Plasmas 3 (1996) Baeva et
al, Phys. Rev. E 74 (2006)
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Two mechanims are involved
Density gradient
Position x (in l)
Hom. plasma
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Two mechanims are involved

• Relativistic Oscillating Mirror
• Doppler effect

Bulanov et al, Phys. Plasmas 1 (1994)
Lichters et al, Phys. Plasmas 3 (1996) Baeva et
al, Phys. Rev. E 74 (2006)

• Coherent Wake Emission
• Plasma oscillations

Quéré et al, PRL 96 (2006)
???
Brunel PRL 59, 52 (1987)
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Two mechanims are involved

• Relativistic Oscillating Mirror
• Doppler effect

Bulanov et al, Phys. Plasmas 1 (1994)
Lichters et al, Phys. Plasmas 3 (1996) Baeva et
al, Phys. Rev. E 74 (2006)

• Coherent Wake Emission
• Plasma oscillations

Quéré et al, PRL 96 (2006)
Brunel PRL 59, 52 (1987)
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Strong analogy of CWE with Recollision mechanism
in atomic or molecular HHG !!!
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Experimental evidence
How do we distinguish these two mechanisms
experimentally ?
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Coherent Wake Emission (1)
CWE Spectral extension max. plasma frequency a
(max. plasma density)1/2
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Coherent Wake Emission (2)
CWE (quasi) linear generation process
CWE signal f (a02) from PIC
Simulations (fixed ions)
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Coherent Wake Emission (2)
CWE (quasi) linear generation process
Harmonic generation on a 1 TW-50 fs Ti-Sa laser
system
Experimental results
F.Quéré et al, Phys. Rev. Lett. 96, 125004 (2006)
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Compressor
Double plasma mirror on a 10 TW-60 fs Ti-Sa
laser 70 TW-20 fs by 2008
DPM chamber
Experimental chamber
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After the double plasma mirror
Overall transmission of DPM 50 Duration and
wavefront unaltered
300 mJ 1010 contrast
Experimental results
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Relativistic Oscillating Mirror (1)
Silica - 3.10 18 W/cm2
Plastic - 8.10 18 W/cm2
Plastic - 3.10 18 W/cm2
Thaury et al, Nature Physics 3 (2007)
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Relativistic Oscillating Mirror (1b)
I3.1018 W/cm2 I8.1018 W/cm2
10-10 contrast Plastic target (wp/wL?15)
Signal (unit. arb.)
Harmonic order
Experimental results
Thaury et al, Nature Physics 3 (2007)
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PIC simulations
PIC simulations reveal a difference in spectral
width between CWE and ROM harmonics
Why? See part 3
Thaury et al, Nature Physics 3 (2007)
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Relativistic Oscillating Mirror (2)
Experimental results
Thaury et al, Nature Physics 3 (2007)
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Intrinsic phase of harmonics from PMs
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Emission time of CWE attosecond pulses
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Emission time of ROM attosecond pulses
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Harmonics intrinsic phase time domain point of
view
Deviations from perfect periodicity lead to
spectral broadening and non-trivial spectral phase
Pulse train
Harmonic order
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Relevant electron trajectories.
in CWE
I2 gt I1
in ROM
?
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Controlling the phase properties of harmonics
Fourier-transform limited
Positively Chirped
Negatively chirped
Fourier-transform limited
CWE
jT jin.jL
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Effect of the chip of the incident laser pulse on
CWE
F.Quéré et al, submitted
See also F.Quéré et al Phys. Rev. Lett. 96,
125004 (2006)
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How to measure the spatial profile ?
Grazing incidence 800 nm AR coating
MCP
10 n15
Laser beam diaphragmed to 30 mm E75 mJ
Dq 14 mrad
Thaury et al, Nature Physics 3 (2007)
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Intrinsic phase in CWE spatial aspects
F.Quéré et al, submitted
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Conclusion

• Two generation mechanisms
• for steep density gradients (i.e. sub-ps laser
  pulses)
• Coherent Wake Emission
• Relativistic Oscillating Mirror

Coherent processes
Spectral and spatial properties can be
coherently controlled through the driving laser
phase
The big experimental challenge How to measure
these attosecond (zepto ?) pulses ?
New challenge for attosecond metrology
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Attosecond measurement Non-linear
autocorrelation by two-photon ionization of He
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Experimental results
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Source properties pulse energy, CWE
MAXIMUM CWE efficiency in PIC simulations
10-4-10-5
Measured energies
I 3.1017 W/cm2 Elaser300 mJ Silica
Energy/harm (µJ)
Conversion efficiency
G.Doumy PhD thesis, Saclay, 2006
Harmonic order
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Coherent Wake Emission
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Effect of the chip of the incident laser pulse
F.Quéré et al, Phys. Rev. Lett. 96, 125004 (2006)
Experimental results
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Distorsions of the reflected waveform
Coherent Wake Emission (CWE)
Relativistic oscillating Mirror (ROM)
I2.1018 W/cm2 - 8nc
I8.1016 W/cm2 - 110 nc
Magnetic field Bz
0
1
2
0
1
2
Time (optical periods)
Time (optical periods)
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Latest results and future directions
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Coherence properties in CWE regime
Experimental result
Harmonic beam (10 n15)
C.Thaury et al, in preparation
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Coherence properties in CWE regime
Laser at focus (measured)
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Coherence properties in CWE regime
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Zooming on CWE, again
Attosecond pulses
Brunel electron bunches
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Two mechanims are involved
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Zooming on CWE
Attosecond pulses
Density gradient
Hom. plasma
Charge density ne-Zni
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Intrinsic phase in CWE experimental evidence
jT jin.jL
I
t or r

• Laser phase jL can be controlled by
• Chirping the laser pulse (temporal phase)
• Moving the best focus (spatial phase)

• Minimizing jT leads to
• Temporally
• minimum spectral width
• Spatially
• minimum divergence