NONLINEAR PROCESSES IN THE EXTREME ULTRAVIOLET REGION USING THE FEL

NONLINEAR PROCESSES IN THE EXTREME ULTRAVIOLET REGION USING THE FEL FERMI@ELETTRA A. Dubrouil, M. Reduzzi, C. Feng, J. Hummert, P. Finetti, O. Plekan, C. Grazioli, M. Di Fraia, V. Lyamayev,A. LaForge, F. Stienkemeier, Y. Ovcharenko, M. Coreno, P. O keeffe, M. Devetta, N. Berrah, K. Motomura, S. Mondal, P. Demekhin, A. Kuleff, L. Cederbaum, K.C. Prince, K. Ueda, C. Callegari, P. Carpeggiani, M. Negro, D. Faccialà, Klaus Bartschat, E. Gryzlova, A. Grum-Grzhimailo, G. Sansone Moscow 28 October 2014

XUV light sources High-harmonic generation Free Electron Lasers 1-10m 0.1-1 km Attosecond time resolution Low photon flux Femtosecond time resolution High photon flux-> nonlinear effects

Experiments 1) XUV nonlinear excitation of neon dimers (FEL) 2) Two-photon double ionization of neon

Motivation: Interatomic Coulombic Decay Mechanism of electronic decay (after inner valence Ionization) dominant in: Hydrogen bonded clusters (H 2 0) n, (HF) n Van der Waals clusters (Ne)n; Ne-Ar; He-He 1 Source of low energy electrons 2 3 L.S. Cederbaum et al. Phys. Rev. Lett. 79, 4778 (1997) T. Jahnke et al. Phys. Rev. Lett. 93, 163401 (2004)

ICD: excitation Mechanism of electronic decay (after inner valence Ionization) dominant in: Hydrogen bonded clusters (H 2 0) n, (HF) n Van der Waals clusters (Ne)n; Ne-Ar; He-He Neon Dimer 1 Source of low energy electrons 1) Ionization by XUV radiation of a 2s electron. 2 3 L.S. Cederbaum et al. Phys. Rev. Lett. 79, 4778 (1997) T. Jahnke et al. Phys. Rev. Lett. 93, 163401 (2004)

ICD: electron correlation Mechanism of electronic decay (after inner valence Ionization) dominant in: Hydrogen bonded clusters (H 2 0) n, (HF) n Van der Waals clusters (Ne)n; Ne-Ar; He-He Neon Dimer 1 Source of low energy electrons 1) Ionization by XUV radiation of a 2s electron. 2 2) a 2p electron fills the 2s hole; emission of a 2p electron from the neighboring atom 3 L.S. Cederbaum et al. Phys. Rev. Lett. 79, 4778 (1997) T. Jahnke et al. Phys. Rev. Lett. 93, 163401 (2004)

ICD: Coulomb explosion Mechanism of electronic decay (after inner valence Ionization) dominant in: Hydrogen bonded clusters (H 2 0) n, (HF) n Van der Waals clusters (Ne)n; Ne-Ar; He-He Neon Dimer 1 Source of low energy electrons 1) Ionization by XUV radiation of a 2s electron. 2 2) a 2p electron fills the 2s hole; emission of a 2p electron from the neighboring atom 3 3) Coulomb explosion of the molecules. timescale 80 fs L.S. Cederbaum et al. Phys. Rev. Lett. 79, 4778 (1997) T. Jahnke et al. Phys. Rev. Lett. 93, 163401 (2004)

Nonlinear excitation of ICD 49,0 2 u + 2 g + 48,5 Ne + (2s -1 )Ne N 2 Energy (ev) 48,0 47,5 23 22 21 2 u + 2 g 2 u 2 g + = 26.888 ev Ne + (2p -1 )-Ne + (2p -1 ) Ne + (2p -1 )Ne E 2s -E 2p =ħω = 26.9 ev 0,002 20 0,000-0,002-0,004 Ne 2 (GS) 2 3 4 5 R (angstrom) P. V. Demekhin et al., Phys Rev Lett 107 (2011).

FERMI@ELETTRA: seeded FEL 3 rd harmonic of Ti:Sa laser or OPA Modulator Radiator N 2 First seeded FEL user facility Energy 1-100 J Photon energy tunability 19-62 ev Pulse duration: 100 fs https://www.elettra.trieste.it/fermi/index.php?n=main.parameter

FERMI@ELETTRA: characteristics Intensity (arb.units) 2,4x10 8 26.40 ev 26.43 ev 2,0x10 8 26.45 ev 26.47 ev 1,6x10 8 1,2x10 8 8,0x10 7 4,0x10 7 Photon energy tunability Δω XUV ~10 mev Number of shots 100 80 60 40 20 Pulse energy stability ΔE = 10% 20% 0,0 26,30 26,35 26,40 26,45 26,50 26,55 26,60 Photon energy (ev) 0 0 10 20 30 40 50 60 70 Energy ( J) Single shot information (energy-spectrum) Ideal source for investigating nonlinear resonant effects in the XUV region!

Low Density Matter (LDM) end station Two supersonic Even-Lavie valves (monomers, cluster, doped clusters) www.elettra.eu/lightsources/fermi/fermi.html Experimental chamber: 1)Velocity map imaging spectrometer 2) Time-of-flight ion spectrometer

Signature of neon dimers: ions N 2 22 Ne + Dimers : 22 Ne 22 Ne + 20 Ne 22 Ne + 20 Ne + 20 Ne 2 + 1) Clear signature of singly ionized neon dimers in the TOF mass spectrum 2) 1% concentration of neon dimers (quadrupole mass spectometer)

Signature of neon dimers : electrons (below ionization threshold of neon) Differences of VMI images (for the same XUV pulse energy); no artefact introduced by the inversion procedure E 0 =27 J l 2 =60.19 nm 20.60 ev S ref =S(l 1 ) l 1 =60.13 nm 20.62 ev l 3 =60.24 nm 20.58 ev DS= S(l 2 )- S(l 1 ) >0 DS= S(l 3 )- S(l 1 ) <0 Differences in the low energy electron region

Single photon ionization of neon dimers Autoionization features in Neon dimers λ 1 =60.13 nm λ 2 =60.19 nm λ 3 =60.24 nm 605 λ 1 60. 13 nm < λ 2 60. 19 nm < λ 3 60. 24 nm S λ 3 < S λ 1 < S λ 2 Trevor et al. J. Chem. Phys. 80 6083 (1984)

Nonlinear excitation of ICD: electrons Photoelectron spectra dominated by ICD for the dimers ħ xuv =26.9 ev N 2 Single photon ionization Ne + ħω Ne + + e?? 2p Competing channel: two-site single photon ionization of neon monomers 2s 1s ħ xuv ħ xuv 2s 1s 2p No clear indication of ICD electrons In the gas jet 1% of neon dimer The photoelectron signal is dominated by the single photon ionization of the monomer P. V. Demekhin et al., Phys Rev Lett 107 (2011).

Nonlinear excitation of ICD: ions N 2 22 Ne + Dimers : 22 Ne 22 Ne + 20 Ne 22 Ne + 20 Ne + 20 Ne 2 + Neon monomer Ne + Neon dimers Ne + 2 Off resonance Weakly dependent on the photon energy Weakly dependent on photon energy On resonance (around 26.9 ev) Weakly dependent on thephoton energy Reduction of neon dimers because ICD and Coulomb explosion

Nonlinear excitation of ICD: dimers vs monomers Ne + 2 Ne + = Ne + 2 Ne + monomers + Ne + dimers Ne + 2 Ne + monomers

Ratio dimers/monomers (theory) Ratio = Ne+ 2 Ne + = Ne + 2 Ne + monomers + Ne + dimers Ne + 2 Ne + monomers (dimers fraction ~ 0.25%) Ratio Ne + 2 / Ne + 5,5x10-3 5,0x10-3 4,5x10-3 4,0x10-3 3,5x10-3 3,0x10-3 2,5x10-3 2,0x10-3 1,5x10-3 1,0x10-3 Assumed dimers fraction ~ 0.25% 5e11(GS=0.870, PiP=0.06) 1e12(GS=0.757, PiP=0.11) 2e12(GS=0.573, PiP=0.18) 26,8 26,9 27,0 Photon energy (ev)

Experiments 1) XUV nonlinear excitation of neon dimers (FEL) 2) Two-photon double ionization of neon

Motivation Resonant (vs nonresonant) two-photon double ionization in neon atoms Autoionizing state ħ 1 2p ħ 2p 2s 1s Nonresonant two-photon ionization Electron yield Angular distribution 2s 1s Resonant two-photon ionization Towards time-resolved dynamics (pump-probe experiment)

Two-photon double ionization of Neon exp exp 1 D 2 44.167 3.204 41.077 41.043 40.963 0 2s 2 2p 4 ( 3 P) Ne III N 2 2s2p 6 3p ħω = 45. 6 ev 0.0968 21.565 0 ħω = 45. 6 ev 2s 2 2p 5 2 P Ne II 0 эв 2s 2 2p 6 Ne I Influence of the autoionization resonance (2s2p63p) on the second ionization step

Two-photon double ionization of Neon exp exp 1 D 2 44.167 3.204 41.077 41.043 40.963 0 2s 2 2p 4 ( 3 P) Ne III N 2 2s2p 6 3p ħω = 45. 6 ev 0.0968 21.565 0 ħω = 45. 6 ev 2s 2 2p 5 2 P Ne II 0 эв 2s 2 2p 6 Ne I Influence of the autoionization resonance (2s2p63p) on the second ionization step

Two-photon double ionization of Neon Exp, ev 57.7 2 S Theory, ev 2.4 2 2 S P 2 4 D P 4 D 4 S 2s2p 5 3p 55.3 55.6 Exp,eV 47.875 0.96 4 0.80-0.82 P, 2 D 4 D 0.50 4 S 0.00 1 S 0 2 P Autoionizing states 44.167 41.077 41.043 40.963 1 D 2 2s 2 2p 4 ( 3 P) Ne III ħω = 56. 5 ev Exp,eV 21.565 0 ev 2s 2 2p 6 Ne I 2s 2 2p 5 2 P Ne II ħω = 56. 5 ev Influence of the autoionization resonance (2s2p53p) on the second ionization step

Conclusions and outloook 1) Nonlinear excitation of neon dimers 2) Two-photon double ionization of neon I) FERMI: pump-probe experiments for time-resolved ICD dynamics II) FERMI: theoretical simulations and data interpretation for two-photon double ionization