john t. costello national centre for plasma science & technology (ncpst)/ school of physical...

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

' FLASH ' - Free Electron LASer in Hamburg

http://www.physics.dcu.ie/~jtc




LIXAM (Orsay): D. Cubaynes, M. Meyer

Universite Paris 06 (PMC): R. Taieb, A. Maquet

DESY (Hamburg): A. Azima, S. Düsterer, 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.)

Acknowledgements


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

Collaboration - Origin


• FLASH (Brief) Overview

• Atoms & Molecules in Intense EUV + NIR Fields Coherent Photoionization Processes in Superposed FieldsOptically probing fragments in EUV dissociated H2

• Two Photon Ionization in Intense EUV Fields

• Next steps

Outline of the Talk


Part 1 - FLASH Overview


300 m

FLASH Overview

• Energy range: ~ 0.3 – 1 GeV ~

6.5 – 60 nm

LaserBunch

CompressorBypass

UndulatorsCollimator

Bunch Compressor

5 MeV 127 MeV 450 MeV 1000 MeV

Accelerating StructuresDiagnostics

FEL Diagnostics

RF-gun


water windowWavelength range (fundamental): 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: ~ 1013

FLASH: Key Performance Indicators

Ackermann et al., Nature Photonics 1 336 (2007)

FEL output builds up from spontaneous emission (photon noise) => SASE – ‘Self Amplified Spontaneous Emission’

O/P Profile and Spectral Distribution

Spectral Fluctuations Temporal Fluctuations


FEL output builds up from spontaneous emission (photon noise) => SASE – ‘Self Amplified Spontaneous Emission’

O/P Profile and Spectral Distribution

Raw EUV Spectrum Corrected EUV Spectrum


Part 2 - Experiments on dilute targets with FLASH

Motivations1. ‘FLASH’ Characterisation

2. Demonstration Experiments

3. Future (Pathfinding)


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 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)


FLASH NIR/Vis and EUV Beam Layout

PG2

BL1

BL3

BL2

visible laser light


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


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


2 colour ATI - Optical Intensity Scaling


Ne: Asymmetry in sideband distribution

€

S n( ) ∝ Sinθ 1+ βP2 Cosθ( )( )0

π



2 colour ATI - Optical Intensity Scaling


Ne: ‘Toy’ SFA Code / Asymmetry in sideband distribution

€

S n( ) ∝ Sinθ 1+ βP2 Cosθ( )( )0

π


Ne: Simulation hFEL = 46 eV

FLASH: 13.7 nm, 10-20 fs, 20µJOL: 800nm, 4ps, 400µJ, 6 x 1011 W/cm2

He 1s2 + hXUV ----> He+ 1s + p

He 1s2 + hXUV + hOL ---> He+ 1s + s, d

Atomic Dichroism in Two colour ATIStrong Polarisation Dependence of Sidebands (Low Field)

Meyer et al., PRL 101 Art. no. 193002 (2008)

Atomic Dichroism in Two colour ATI - He

Low Optical Laser Field High Optical Laser Field

P. Theory: A Grum-Grzhimailo et al. SPA: A Maquet/ R Taieb

Meyer et al., PRL 101 Art. no. 193002 (2008) €

SHen( ) ∝ Sinθ Cos2θ( )

0

π


€

dσ n( )

dθ

⎛

⎝ ⎜

⎞

⎠ ⎟= Jn

2 r α .

r K ( )

dσ 0( )

dθ

⎛

⎝ ⎜

⎞

⎠ ⎟r E k

() = 3Sd + (5Ss + Sd) cos2Ss/Sd =1.25 ± 0.3

Atomic Dichroism in Two colour ATI - Kr

FLASH: 13.7 nm, 10-20 fs, 20µJOL: 800nm, 4ps, 6 x 1011 W/cm2


AD in TC-ATI:Ne, Kr, Xe: work in progress

Atomic Dichroism in 2 colour ATI - Ne+


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….?



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-





13.7 nm (pump) + 400 nm (probe)

Low Intensity(0.5 mJ/120 fs)

High Intensity(1.5 mJ/120 fs)


Dynamics - more to do - jitter limited.


expt.fit

risetime= 500 fs


Xe ionization in intense EUV fields


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



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)


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’


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


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


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

2. Beyond 2009: Seeding, fs jitter, angle resolved PES,…

3. LCLS/XFEL/SPRING-8/NLS………..


john t. costello national centre for plasma science & technology (ncpst)/ school of physical...

Documents

intense euv fields

hamburg slide

intense euv optical

nm fields

flash http

flash motivations

flash characterisation

intense optical fields