Transcript - School of Physical Sciences
Two Colour and Two Photon Ionization Processes in Intense
EUV
and
Optical
Fields at F
LAS
H
John T. Costello
National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University www.physics.dcu.ie/~jtc
' F LAS H ' - Free Electron LAS er in H amburg
Ultrafast Imaging Workshop, Ischia May 3, 2009
Acknowledgements LIXAM (Orsay):
D. Cubaynes, M. Meyer
Universite Paris 06 (PMC):
R. Taieb, A. Maquet
DESY (Hamburg)
: A. Azima, S. D üsterer, P. Radcliffe, H. Redlin, W-B Li, J. Feldhaus
PTB (Berlin):
A. A. Sorokin, M. Richter
Moscow State University
: A. N. Grum-Grzhimailo, E. V. Gryzlova, S. I. Strakhova
Queen’s University Belfast:
Hugo van der Hart
Dublin City University:
J. Dardis, P. Hayden, P. Hough, T. Kelly, V. Richardson, E. T. Kennedy, J. T. Costello Thanks to AG Photon (R Treusch et al.) & AG Machine (M Yurkov et al.) Ultrafast Imaging Workshop, Ischia May 3, 2009
Collaboration - Origin
Collaboration grew out of EU RTD Project: HRPI-CT-1999-50009
Title: “X-Ray FEL Pump Probe Facility” Partners: Orsay, DCU, Lund, MBI, BESSY & DESY
Ultrafast Imaging Workshop, Ischia May 3, 2009
Outline of the Talk
•
FLASH (Brief) Overview
•
Atoms & Molecules in Intense EUV + NIR Fields
Coherent Photoionization Processes in Superposed Fields Optically probing fragments in EUV dissociated H 2
•
Two Photon Ionization in Intense EUV Fields
•
Next steps
Ultrafast Imaging Workshop, Ischia May 3, 2009
Part 1 - FLASH Overview
Ultrafast Imaging Workshop, Ischia May 3, 2009
FLASH Overview
RF-gun Diagnostics Accelerating Structures Laser 5 MeV Bunch Compressor 127 MeV Collimator Undulators Bunch Compressor 450 MeV 1000 MeV 300 m •
Energy range: ~ 0.3 – 1 GeV
~ 6.5 – 60 nm
Bypass FEL Diagnostics Ultrafast Imaging Workshop, Ischia May 3, 2009
FLASH: Key Performance Indicators Wavelength range (fundamental): water window
6 - 60 nm
FEL harmonics (@13.7 nm): 3 rd : 4.6 nm (270 eV) 5 rd : 2.7 nm (450 eV) Spectral width (FWHM): 0.5-1 % Pulse energy: up to 70 µJ (average), 170 µJ (peak) Pulse duration (FWHM): 10-50 fs Peak power (fundamental): Few GW Average power (fundamental): 0.1 W (up to 3000 pulses / sec) Photons per pulse: ~ 10 13
Ackermann et al., Nature Photonics
1
336 (2007)
O/P Profile and Spectral Distribution
FEL output builds up from spontaneous emission (photon noise) =>
SASE – ‘Self Amplified Spontaneous Emission’
Spectral Fluctuations Temporal Fluctuations Ultrafast Imaging Workshop, Ischia May 3, 2009
O/P Profile and Spectral Distribution
FEL output builds up from spontaneous emission (photon noise) =>
SASE – ‘Self Amplified Spontaneous Emission’
Raw EUV Spectrum Corrected EUV Spectrum Ultrafast Imaging Workshop, Ischia May 3, 2009
Part 2 - Experiments on dilute targets with FLASH
Motivations
1. ‘FLASH’ Characterisation 2. Demonstration Experiments 3. Future (Pathfinding)
Ultrafast Imaging Workshop, Ischia May 3, 2009
Atoms & Molecules in Intense EUV + Optical (800/400 nm) fields
1. Photoionization of rare gas atoms dressed by intense optical fields 2. Optical probing EUV dissociated H
2
Summary of AMOP@FLASH http://hasylab.desy.de/science/user_collaborations/amopflash Photoionization Experiments with the Ultrafast EUV Laser FLASH - Free Electron Laser in Hamburg J T Costello, J Phys Conf Ser
88
Art No 012057 (2007) C. Bostedt et al.,
Experiments at FLASH,
Nucl. Inst. Meth. in Res. A
601
108-122 (2009) Ultrafast Imaging Workshop, Ischia May 3, 2009
FLASH NIR/Vis and EUV Beam Layout
BL2 BL3 BL1 PG2 visible laser light
Ultrafast Imaging Workshop, Ischia May 3, 2009
Two colour ATI/ Laser Assisted PES
Superposition of visible and VUV pulses in a noble gas jet
Schins et al. PRL
73
, 2180 (1994)
Electron Spectrometer VUV Visible fs laser pulse
Sideband intensity very Sensitive to overlap
Ar(IP)
gas jet
E.S. Toma et al. PRA
62
061801 (2000)
h
w
ir =1.55eV
15.76 eV
Two colour ATI/ Laser Assisted PES
Experimental Layout at FLASH - (EU-RTD)
P. Radcliffe, et al., Nucl. Instr. and Meth. A
83
, 516-525 (2007)
Two colour ATI/ Laser Assisted PES
Sideband number/intensity depend strongly on EUV/NIR overlap by comparison with theory
we are able to determine relative time delay to better than 100 fs
550 fs
1. New ultrafast EUV-modulated optical-reflectivity methods
C. Gahl et al., Nature Photonics
2
165-169 (2008) T. Maltezopoulos et al., New J Phys
10
Art. No. 033026 (2008)
2. ‘TEO’
A. Azima et al., APL.
(In Press 2009) P. Radcliffe, et al., Nucl. Instr. and Meth. A
83
, 516-525 (2007) P Radcliffe, et al., APL
90
131108 (2007)
Two colour ATI ‘Soft Photon’
‘n’ photon ATI cross-section
d
d
k k
0
J n
2
d
d
E k
One photon cross-section
F
w
L
- Classical excursion vector of an electron in a laser field of amplitude
F K
- Momentum transfer After a little work………….sideband strength is given by an expression like……
S
0
Sin
1
P
2
Cos
J
2
n
0
k n Cos
d
J n Bessel function (first kind order ‘n’) k n - Shifted wavenumber of the ejected electron = - Usual asymmetry parameter 2 w
IP
w
FEL
n
w
L
A Maquet and R Taieb, J. Mod. Opt.
54
1847 (2007)
Two colour ATI - Z Scaling
800 nm Ti-Sa 1.55 eV/ 120 fs FLASH h ~ 93 eV 20 J/pulse
Two colour ATI - Z Scaling
Intesnity ratio of n= 1:2 sidebands - Model vs Experiment Experiment ‘Soft Photon’ Fitted 800 nm intensity ~ 5 x 10 11 W.cm
-2 Ultrafast Imaging Workshop, Ischia May 3, 2009
2 colour ATI - FEL Wavelength Scaling
FEL + 800 nm . SB Ratio - Comparison of SPA with Experiment Ultrafast Imaging Workshop, Ischia May 3, 2009
2 colour ATI - Optical Intensity Scaling
Ne: Asymmetry in sideband distribution
S
Sin
1
P
2
Cos
J n
2 0
k n Cos
d
0 Ultrafast Imaging Workshop, Ischia May 3, 2009
2 colour ATI - Optical Intensity Scaling
Ne: ‘Toy’ SFA Code / Asymmetry in sideband distribution
S
Sin
1
P
2
Cos
J n
2 0
k n Cos
d
0 Ne: Simulation h FEL = 46 eV
Atomic Dichroism in Two colour ATI
Strong Polarisation Dependence of Sidebands (Low Field) FLASH: 13.7 nm, 10 20 fs, 20µJ OL: 800nm, 4ps, 400µJ, 6 x 10 11 W/cm 2
He 1s 2 He 1s 2 + h XUV + h XUV ----> He + + h OL 1s + ---> He + p 1s + s, d Meyer et al., PRL
101
Art. no. 193002 (2008)
Atomic Dichroism in Two colour ATI - He Low Optical Laser Field High Optical Laser Field
( ) = 3S d S s /S d + (5S s =1.25 ± 0.3
+ S d ) cos 2
P. Theory:
A Grum-Grzhimailo et al.
Meyer et al., PRL
101
S He
d
d
J n
2
d
d
E k
0
Sin
Cos
2
J n
2 0
k n Cos
d
SPA:
A Maquet/ R Taieb
Atomic Dichroism in Two colour ATI - Kr
AD in TC-ATI: Ne, Kr, Xe: work in progress
FLASH: 13.7 nm, 10 20 fs, 20µJ OL: 800nm, 4ps, 6 x 10 11 W/cm 2
Ultrafast Imaging Workshop, Ischia May 3, 2009
Atomic Dichroism in 2 colour ATI - Ne +
Sequential Ionization
‘Work in progress’ - but we can begin to think about studying isonuclear trends…….
Ultrafast Imaging Workshop, Ischia May 3, 2009
Summary - Two Colour ATI
1. Demonstrated interference free SBs to high order, polarisation control, laser and FEL parameter dependencies & SBs in atomic and ionic targets 2. At low optical intensities 2nd OPT & SPA agree 3. Beyond He we really need to measure angular distributions to try to unravel the ‘l’ channels… 4. SPA works well at high intensities but the number of open high angular momentum channels is a challenge for other approaches such as R-Matrix Floquet (HvdH) 5. Is there really value in going beyond SPA here ? Does the residual ion core atomic structure really matter….?
Ultrafast Imaging Workshop, Ischia May 3, 2009
Optical Probing of H
2
Dissociation Demonstration Experiment
Ultrafast Imaging Workshop, Ischia May 3, 2009
Optical Probing of H
2 < 100 fs
Dissociation
1) H 2 + h (FEL) --> H + H*
FEL : 13.7 nm, 90.5 eV h
VUV
2) H* + h (las) --> H + + e -
Opt.Las. : 400 nm, 3.1 eV H + + H + H + + H(nl) H + + H(1s) H(1s) + H(1s)
Ultrafast Imaging Workshop, Ischia May 3, 2009
Optical Probing of H
2
Dissociation
13.7 nm (pump) + 400 nm (probe) High Intensity (1.5 mJ/120 fs) Low Intensity (0.5 mJ/120 fs) Ultrafast Imaging Workshop, Ischia May 3, 2009
Optical Probing of H
2
Dissociation
Dynamics - more to do - jitter limited.
expt.
fit
risetime = 500 fs
Ultrafast Imaging Workshop, Ischia May 3, 2009
Xe ionization in intense EUV fields
Ultrafast Imaging Workshop, Ischia May 3, 2009
4d two photon direct ionization
FEL only. h
~ 93 eV Xe + 2h
Xe + + e Replace PIS by MBES - First evidence of inner-shell TPI
Ultrafast Imaging Workshop, Ischia May 3, 2009
Part 3. Current and Future Interests
Two Colour
Resonant
Photoionization Processes 1. To date we have looked only at one and two colour
non-resonant
processes 2. Next phase - FEL tunable and so we can explore
resonant two colour
processes where inner shell electrons dominate Ultrafast Imaging Workshop, Ischia May 3, 2009
Kr (3d 9 4d) 2 Photon Resonance Auger
Kr + 3d 9 2 D 5/2
4d
92.0eV
Auger
Kr + 4p 4 4d, 5d ?
Expt. June 2009 (Hopefully) MLM - 3 degree incidence VUV 46.1 eV
Kr 3d 10 4s 2 4p 6 Ultrafast Imaging Workshop, Ischia May 3, 2009
Kr (3d 9 4d) DOR-Auger First Effort: Resonant Auger Spectrum
Kr + 3d 9 2 D 5/2
4d
5p 92.0eV
Auger
1.55 eV Kr + 4p 4 4d, 5d ?
XUV 13.9 nm FEL+las FEL 4s 4p SB
Kr 3d 10 4s 2 4p 6 TOF (ns)
Next Expt: eV) h
FEL (89 eV) + h
OL (3.1
Ultrafast Imaging Workshop, Ischia May 3, 2009
Experiments post-upgrade
Upgrade -
Optical Parametric Amplifier
- (fs OPA)
Laser coupling/spectroscopy of autoionization states 'Autler-Townes' meets ‘Codling-Madden’
Ultrafast Imaging Workshop, Ischia May 3, 2009
Tunable Optical Laser - Laser Coupling of autoionization states - 'Autler Townes' Autoionizing Resonances - He
Bachau & Lambropoulos, PRA (1986) Themelis, Lambropoulos, Meyer, JPB (2005) ‘New Knobs’ 1.
2.
Laser Frequency Laser Intensity Laser Coupled Autoionising State Dynamics Ultrafast Imaging Workshop, Ischia May 3, 2009
FLASH - Technical Developments OPA Upgrade Synchronisation Seeding with HHs -
0.01 - 1 mJ/ 0.1 - 20 ps New FIR Undulator (THz) Full coherence Stabilisation Synchroniosation Ultrafast Imaging Workshop, Ischia May 3, 2009
In Conclusion
1. To date we have looked only at one and two colour
non resonant
photoionization processes 2. Now -
FEL easily tunable
- we can explore
resonant two colour
processes where inner shell electrons dominate
3. Study fragmentation and ionization from vibrationally excited/selected wavepackets in simple molecules
4.
Beyond 2009: Seeding, fs jitter, angle resolved PES,…
5.
LCLS/XFEL/SPRING 8/NLS………..
Ultrafast Imaging Workshop, Ischia May 3, 2009