John T. Costello National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University www.physics. dcu . ie/~jtc Two Colour and Two Photon Ionization Processes in Intense EUV and Optical Fields at FLASH Ultrafast Imaging Workshop, Ischia May 3, 2009 LASH ' - Free Electron LASer in Hamburg
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John T. Costello National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University jtc Two.
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John T. Costello
National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University
www.physics.dcu.ie/~jtc
Two Colour and Two Photon Ionization Processes in Intense
1. Photoionization of rare gas atoms dressed by intense optical fields
2. Optical probing EUV dissociated H2
Summary of AMOP@FLASHhttp://hasylab.desy.de/science/user_collaborations/amopflash
Photoionization Experiments with the Ultrafast EUV Laser FLASH - Free Electron Laser in HamburgJ 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
PG2
BL1
BL3
BL2
visible laser light
Ultrafast Imaging Workshop, Ischia May 3, 2009
E.S. Toma et al. PRA 62 061801 (2000)
Two colour ATI/ Laser Assisted PES
ElectronSpectrometer
gas jet
Visiblefs laser pulse
VUV
Superposition of visible and VUV pulses in a noble gas jet
Ar(IP) 15.76 eV
hir =1.55eV
Sidebandintensity very
Sensitive tooverlap
Schins et al. PRL 73, 2180 (1994)
P. Radcliffe, et al., Nucl. Instr. and Meth. A 83, 516-525 (2007)
Two colour ATI/ Laser Assisted PESExperimental Layout at FLASH - (EU-RTD)
Two colour ATI/ Laser Assisted PES
P. Radcliffe, et al., Nucl. Instr. and Meth. A 83, 516-525 (2007) P Radcliffe, et al., APL 90 131108 (2007)
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 2. ‘TEO’C. Gahl et al., Nature Photonics 2 165-169 (2008) A. Azima et al., APL.T. Maltezopoulos et al., New J Phys 10 Art. No. 033026 (2008) (In Press 2009)
A Maquet and R Taieb, J. Mod. Opt. 54 1847 (2007)
Two colour ATI - ‘Soft Photon’
€
S n( ) ∝ Sinθ 1+ βP2 Cosθ( )( )0
π
∫ Jn2 α 0knCosθ( )dθ
€
dσ n( )
dθ
⎛
⎝ ⎜
⎞
⎠ ⎟=
k
k0
Jn2 r
α .r K ( )
dσ 0( )
dθ
⎛
⎝ ⎜
⎞
⎠ ⎟r E k
€
rα=
rF
ωL
- Classical excursion vector of an electron in a laser field of amplitude
€
rF
One photoncross-section
‘n’ photon ATIcross-section
€
rK =
r k −
r k 0( ) - Momentum transfer
Jn - Bessel function (first kind order ‘n’)
After a little work………….sideband strength is given by an expression like……
kn - Shifted wavenumber of the ejected electron =
€
2 ωIP + ωFEL + nωL( )
- Usual asymmetry parameter
Two colour ATI - Z Scaling
800 nm Ti-Sa1.55 eV/ 120 fs
FLASHh ~ 93 eV20 J/pulse
Two colour ATI - Z Scaling
Fitted 800 nm intensity~ 5 x 1011 W.cm-2
Ultrafast Imaging Workshop, Ischia May 3, 2009
Intesnity ratio of n= 1:2 sidebands - Model vs Experiment
‘Soft Photon’
Experiment
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
Ultrafast Imaging Workshop, Ischia May 3, 2009
Ne: Asymmetry in sideband distribution
€
S n( ) ∝ Sinθ 1+ βP2 Cosθ( )( )0
π
∫ Jn2 α 0knCosθ( )dθ
Ultrafast Imaging Workshop, Ischia May 3, 2009
2 colour ATI - Optical Intensity Scaling
Ultrafast Imaging Workshop, Ischia May 3, 2009
Ne: ‘Toy’ SFA Code / Asymmetry in sideband distribution
Sequential Ionization ‘Work in progress’ - but we can begin to think about studying isonuclear trends…….
Summary - Two Colour ATI1. 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
Ultrafast Imaging Workshop, Ischia May 3, 2009
Demonstration Experiment
Optical Probing of H2 Dissociation
< 100 fs
hVUV
H(1s) + H(1s)
H+ + H(1s)
H+ + H(nl)
H+ + H+
FEL : 13.7 nm, 90.5 eV
1) H2 + h(FEL) --> H + H*
Opt.Las. : 400 nm, 3.1 eV
2) H* + h(las) --> H+ + e-
Optical Probing of H2 Dissociation
Ultrafast Imaging Workshop, Ischia May 3, 2009
Ultrafast Imaging Workshop, Ischia May 3, 2009
Optical Probing of H2 Dissociation
13.7 nm (pump) + 400 nm (probe)
Low Intensity(0.5 mJ/120 fs)
High Intensity(1.5 mJ/120 fs)
Ultrafast Imaging Workshop, Ischia May 3, 2009
Dynamics - more to do - jitter limited.
Optical Probing of H2 Dissociation
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
Part 3. Current and Future InterestsTwo 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
Ultrafast Imaging Workshop, Ischia May 3, 2009
Kr 3d10 4s2 4p6
Kr+ 3d9 2D5/2
4d
VUV46.1 eV
Auger
Kr+ 4p4 4d, 5d
?
92.0eV
Expt. June 2009 (Hopefully)
MLM - 3 degree incidence
Kr (3d94d) 2 Photon Resonance Auger
First Effort:Resonant Auger Spectrum
TOF (ns)
4p4s
SB
FEL+las
FEL
Kr (3d94d) DOR-Auger
Next Expt: hFEL (89 eV) + hOL(3.1 eV)
Ultrafast Imaging Workshop, Ischia May 3, 2009
Kr 3d10 4s2 4p6
Kr+ 3d9 2D5/2
4d
5p
XUV13.9 nm
Auger
Kr+ 4p4 4d, 5d
?
92.0eV
1.55 eV
Upgrade - Optical Parametric Amplifier - (fs OPA)
Experiments post-upgrade
Laser coupling/spectroscopy of autoionization states - 'Autler-Townes' meets
‘Codling-Madden’
Ultrafast Imaging Workshop, Ischia May 3, 2009
Bachau & Lambropoulos, PRA (1986)Themelis, Lambropoulos, Meyer, JPB (2005)
‘New Knobs’1. Laser Frequency2. Laser Intensity
Tunable Optical Laser - Laser Coupling of autoionization states - 'Autler Townes' Autoionizing Resonances - He
Laser Coupled AutoionisingState Dynamics
Ultrafast Imaging Workshop, Ischia May 3, 2009
FLASH - Technical Developments
OPA Upgrade - 0.01 - 1 mJ/ 0.1 - 20 ps
Synchronisation - New FIR Undulator (THz)
Seeding with HHs - 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
• 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