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Attosecond Metrology. A method for attosecond pulse characterisation. Adam Wyatt 1. Eadweard Muybridge’s Horse in Motion. Ian Walmsley 1 Laura Corner 1 A. Monmayrant John Tisch et al 2 Eric Cormier 3 Louis F. DiMauro 4. 1 Clarendon Laboratory, University of Oxford - PowerPoint PPT Presentation
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Attosecond MetrologyA method for attosecond pulse characterisation
Adam Wyatt1
Ian Walmsley1
Laura Corner1
A. MonmayrantJohn Tisch et al2
Eric Cormier3
Louis F. DiMauro4
1Clarendon Laboratory, University of Oxford2Blackett Laboratory, Imperial College3Centre Lasers Intenses et Applications, Universite Bordeaux4Brookhaven National Laboratory
Eadweard Muybridge’s Horse in Motion
Outline
• Motivation
• Analytic Representation of Optical Pulses
• SPIDER Generalisation & Implementation
• High Harmonic Generation
• XUV SPIDER Variants
• Research Tasks
• Conclusion
Overview of presentation
MotivationSuccess of Femtoscience – applications for Attoscience
Pump Probe Experiments – Advanced Flash Photography
• To capture event, need to have flash shorter than event.
• If exact detail of probe pulse known, pulse only needs to be comparable in duration to event in interest.
Success of Femtoscience Applications for Attoscience
• Tracking molecular motion in chemical reactions (femtochemistry)
• Detection & control of coherent processes.
• Micromachining
• Nobel Prizes!!!
• Tracking electronic motion
• Surface science
• ????
MethodsCurrent pulse characterisation methods
Non-Interferometric Interferometric
Tomographic Chronocyclic Tomography2:Reconstructs 2D density function from 1D data sets.
SPIDER4:Reconstructs spectral phase from 1D data set using a direct (non iterative) algorithm.
Spectrographic FROG3:Reconstructs pulse shape from 2D data set using iterative algorithm.
Different classes of characterisation methods and some examples1:
1I. A. Walmsley & V. Wong, J Opt Soc Am B,13(11), 1996
2M. Beck et el, Opt Lett, 18(23), 1993
3R. Trebino et el, Rev Sci Inst, 68(9), 1997
4L. Gallmann et el, Opt Lett, 24(18), 1999
2 Beam Interferometery
2 2
1 201,02 01,02 01 02
1 201 02
1 01 2 02 01 02
; , ; ;
2 ; ;
cos ; ;
I t E E
E E
t t
2 001,02 01,0
2
2 022 1 01 01; ; ,,; , E E tt tI 1 01 01; ,E t
Generalised Interferometer Spectrum
Spectrometer
Beamsplitter
~2/(t01-t02)
I()
2 02 02; ,E t
Carrier Frequency
dc ac aci iI I I e I e
1 2
2 2
1 2
1 2
dc
ac
I E E
I E E e
ad acccFT I I t I tI t tt t
How to extract the phase information
~2/
I()
t
I tFourier Transform
2 1 argfilter iIFT I e
filter
ac i
I H t I t
FT I e
What is needed for SPIDER
0
0 0
0 0 0
0 01
0
2
1n
n n
2
T
Spectral Shear
T
t
2/T
Nyquist:
Noise:
2
T
Sampling Interval
Classic SPIDERExperimental Set-up
XUV SPIDER
01 02
01 02
02
Generating the shear in the XUV
31 33 35 37n
(n)
31 33 35 37
2 1n n n
Example
• 30fs driving pulses at 800nm ~ 209 x1012 rad s-1
• 13nm corresponds to n = 61• 1nm bandwidth at 13nm t = 275as• Shear at driving freq. = / 61 = 1.2nm
XUV SPIDERSPIDER method for HHG radiation
SEA-XUV SPIDERSEA-SPIDER method for HHG radiation
Fourier Transform
2 2' '
' 2 2( , ) ', ',kx kx x
i ii x L LI x E x E x e e
SPIDER Adv.Comparisons of different techniques
SPIDER Pros: SPIDER Cons:
• Simple, direct inversion algorithm.
• Possible real time diagnostics.
• Possible spatial information.
• Higher SNR (photoelectron spectrometer)
→ Increased accuracy
→ Single shot capability
• Pulse train statistics.
• Self-consistency checks.
• Split driving pulses – lower intensity lower harmonic number.
• Need to generate two identical, spectrally sheared pulses of high intensity & stability.
Different SPIDER Adv.Comparison of XUV-SPIDER and SEA-SPIDER
XUV-SPIDER SEA XUV-SPIDER
Pros: • Rapid Update rates – real time diagnostics.
• Pulses see same section of gas.
• No intensity limit on driving pulses.
• Lower resolution for spectrometer.
• Measure spectral phase at different spatial co-ordinates.
Cons: • Maximum intensity of driving pulses due to ionisation. Maximum harmonic number.
• High resolution spectrometer required.
• Average over spatial phase.
• More data – slower update rates.
• Pulses see different gas densities.
Simulated ResultsSimulated HHG data and XUV SPIDER reconstruction
31 33 35 37-15
-10
-5
0
5
10
Original and Reconstruction of Phase Of Harmonics
Harmonic Order
Pha
se /r
ad
Rescaled Harmonic Spectrum
Phase from 800nm driving pulse
Phase from 800.5nm driving pulse
Reconstructed Phase
-10 -8 -6 -4 -2 0 2 4 6 8 100
1
2
3
4
5Temporal Profiles of Attosecond Pulse Trains
time /fs
Inte
nsity
/arb
. uni
ts
Fourier Transform Limited (FTL)
Simulated Profile
Reconstructed Profile
31 33 35 37-15
-10
-5
0
5
10Original and Reconstruction of Phase Of Harmonics
Harmonic Order
Pha
se /r
ad
-10 -8 -6 -4 -2 0 2 4 6 8 100
1
2
3
4
5Temporal Profiles of Attosecond Pulse Trains
time /fs
Inte
nsity
/arb
. uni
ts
Rescaled Harmonic Spectrum
Phase from 800nm driving pulse
Phase from 802.5nm driving pulse
Reconstructed Phase
Fourier Transform Limited (FTL)
Simulated Profile
Reconstructed Profile
Generating the carrier frequencyCan do – need to improve!
Fringes 2D Fourier Transform
Generating the shearSome ideas still to be tested
Bi-Mirror / Knife edge 4-f Knife edge / Full puls shaping
AOPDF Pulse Shaping
Hard – too large bandwidthLow power output (high losses)
Easily implementedLimitations
Osc. AOPDF Amp.
HCFHHGMetrology
Research TasksWhat to do?
• Simulate HHG with two driving pulses directly (c.f. combing spectra from individual pulse
simulations).
• Find optimal shear and time delay for typical noise parameters.
• Test XUV-SPIDER for shorter pulses (5 fs) via simulation.
• Test how different driving pulses can be.
• Test generating shear
Conclusions
• Applications & motivation for Attoscience. Success of femtoscience.
• SPIDER technique. What is needed (carrier frequency & time delay) Conventional implementation.
• XUV SPIDER. How to create shear via HHG.
• Pros & Cons of SPIDER. Lots of good points, limited by creating sheared pulses.
• Still more to do
• Promising outlook!
What have we learnt?