Atomic Photoionization Dynamics in Intense Radiation Fields

Transcription

1 Atomic Photoionization Dynamics in Intense Radiation Fields M. Meyer LIXAM, Centre Universitaire Paris Sud, Orsay France - Introduction - Two-Color (XUV + NIR) Experiments - intense NIR - intense XUV - Time-resolved Pump-Probe Experiments - Conclusion Institute of Nuclear Physics, MSU, Moscow, November 17, 2009

2 Free Electron Lasers in Hamburg Hamburg DESY DESY RF-gun 300m 3.4km Exp. FLASH European > 2005 > 2015 X-FEL

3 Free Electron Lasers in Hamburg DESY RF-gun 300m 10 9 Exp FLASH > 2005

4 FLASH (Free electron LASer in Hamburg) Ackermann et al., Nature Photonics 1, 336 (2007) RF-gun Diagnostics Accelerating Structures Collimator Undulators Laser Bunch Compressor Bunch Compressor 5 MeV 127 MeV 450 MeV 1000 MeV 300 m Bypass FEL Diagnostics LINAC : 1 GeV 30 m fixed-gap undulator macro-bunch at 10 Hz log (power) low gain exponential gain (high-gain linear regime) P(z) = P o exp(z/l gain ) non-linear gain ~ 10 5 > 30 bunches, 1 μs separation saturation length ~ 10 L gain

5 SASE (Self Amplified Spontaneous Emission) Ackermann et al., Nature Photonics (2007) FEL output builds up from spontaneous emission (photon noise) intensity (arb. units) λ 0 = 32.2 nm b.w. = % ΔE = 200 mev λ 0 = 13.7 nm λ (nm) Spectral fluctuation Temporal fluctuation

6 Free Electron Laser Sources FLASH LCLS (Stanford, CA) SCSS (Japan) European XFEL (Hamburg) 6-60 nm (0.5-1% b.w.) ( ev) 5 Hz (up to 60 bunches) µj (average) nm ( kev) 120 Hz / 60 Hz > 100 µj nm ( kev) 10 Hz (3000 bunches) > 100 µj fs ~ photons/pulse > W / cm fs / 500 fs photons/p > W / cm 2 < 100 fs photons/p > W / cm 2

7 SCIENCE at FLASH - Intense Source ~ photons/pulse Studies on dilute targets (HCI, m-sel. cluster, HeH+ ) - Short Pulses ΔT = fs ~ μj (> W/cm 2 ) - Short Wavelengths 6-60 nm ( ev) Time-resolved studies (Two-Color Pump-Probe) Non-Linear Processes (Multi-photon) Innershell Ionization

8 Photoionization Dynamics A + + e - hν 2 : fs laser hν 1 : FEL >10 14 W / cm 2 >10 12 W / cm 2 hν 2 hν 1 A I) Non-linear processes: - Two-photon ionization - Photoionization of dressed atoms 2) Dynamics in strong fields Strong field: A + hν 1 + hν 2 A + + e - One-step process!!

9 Relaxation Dynamics of Core Resonances A** hν 2 : fs laser hν 1 : FEL >10 14 W / cm 2 >10 12 W / cm 2 A* hν 2 hν 1 3) Non-linear processes: - Two-photon resonances - Coupling of Autoionizing States hν 1 A hν 2

10 Energy Photodissociation Dynamics Time-resolved development of the electronic structure during dissociation or chemical reactions PAD Excitation of core electrons XFEL AB A* B R(A-B) element specific «Pump»or «Probe»

11 Experiments at FLASH BL1 PG2 BL3 BL2 visible laser light

12 FLASH + Optical Laser linac e - FEL bending magnet FEL to user electrons visible synchrotron radiation Ti:Saph laser : 800 nm 120 fs, μj -->(120 fs - 4 ps, 2 mj) Nd:YLF pump laser : 523 nm 12 ps, 600 μj opt. laser to user TTF clock from injector rack 300 m long cables synchroscan streak camera slow feedback goal: drift < ps / h Max-Born-Institut, Berlin I. Will, H. Redlin

13 Two-Color Photoelectron Spectroscopy MBES: Magnetic Bottle Electron Spectrometer (4π collection angle) J.H.D. Eland et al. PRL90,53003 (2003) TOF : 65 cm thermopile photodiode phosphor screen e - MCP μ - metal solenoid T = 6 x 10-4 T grids - U(ret) permanent magnet T= 0.5 T FEL Opt.Las.

14 Two-color experiments Intense optical field: Above Threshold Ionization of rare gases

15 Above Threshold Ionization of Rare Gases FLASH: 25.5 nm, 20 μj, 50 μm focus, 20 fs Opt. Laser : 800 nm, 20μJ, 50 μm focus, 12 ps 2 x W/cm 2 IR e - XUV He + He Toma et al. PRA 62, (2000) Radcliffe et al. APL 90, (2007) Maquet/Taieb, J.Mod.Opt. 54, 1847 (2007)

16 Temporal resolution / Synchronization : ATI Average Mode: Cross Correlation Curve Single Shot Mode: Photoelectron spectra FWHM = 600 ± 70 fs ΔT FEL =20fs ΔT O.L. =120fs 0 ps temporal resolution ΔT = 600 fs Jitter (FEL) = 550 ± 80 fs temporal resolution ΔT 50 fs only for overlapping pulses M. Meyer et al. PRA R (2006), P. Radcliffe, et al., APL (2007) A. Maquet, R. Taïeb, J. Mod. Opt (2007)

17 Polarization control in two-color photoionization I OL < W/cm 2 I OL > W/cm 2 M. Meyer et al., PRL 101, (2008) He 1s 2 + hν XUV ----> He + 1s + εp He 1s 2 + hν XUV + hν OL ---> He + 1s + εs, εd

18 Polarization control: two-color two-photon FLASH: 13.7 nm, fs, 20µJ OL: 800nm, 4ps, 70µJ, 8 x W/cm 2 σ(θ) = 3S d + (5S s + S d ) cos 2 θ Two-photon ionization He 1s 2 + hν XUV + hν OL ---> He + 1s + εs, εd S s / S d = 1.25 ± only d - emission times more s than d

19 Polarization control: two-color multi-photon FLASH: 13.7 nm, fs, 20µJ OL: 800nm, 4ps, 400µJ, 6 x W/cm 2 Soft-Photon Approximation hν OL << E kin He 1s 2 + hν XUV + hν OL ---> He + 1s + εl higher l 0(s), 2(d) A. Maquet, R. Taieb, J. Mod. Opt. 54, 1847 (2007)

20 Temporal Control of ATI FLASH: 13.7 nm, 30 μj, 50 μm focus, 20 fs Opt. Laser : 800 nm, 4 mj, 50 μm focus, 120 fs - 4 ps IR e - Xe 5p XUV Xe + Xe Kinetic Energy (ev) Delay time (ps) I n t 4 x W/cm 2

21 ATI : Strong NIR Dressing Field (Xe) Optical laser: > W/cm 2 Xe 5p -1 2 P 1/2 Time-of-flight (ns). SB3 2 P 3/2 SB12 Multi-photon processes hν(800nm) = 1.5eV ΔE( 2 P 3/2-2 P 1/2 ) = 1.3eV

22 ATI : Strong NIR Dressing Field (Ne) FEL: 26.9nm (46 ev) Laser: 800nm, 1.8mJ, 100fs 3x10 13 W/cm 2 Soft-Photon Approximation 5x10 11 W/cm 2 He Ne 2p -1 2x10 12 W/cm 2 Multi-photon processes A. Maquet, R. Taieb, J. Mod. Opt. 54, 1847 (2007)

23 XFEL: Laser-assisted resonant Auger decay Laser Coupling of Final Ionic States Ne + 1s -1 2s 2 2p 6 870eV XFEL OL Ne ++ 2p 4 Ne 1s 2 2s 2 2p 6 Southworth et al. PRA 52, 1272 (1995)

24 XFEL: Laser-assisted resonant Auger decay Laser Coupling of Final Ionic States A. Kazansky, N. Kabachnik, J. Phys. B (2009) Ne + 1s -1 2s 2 2p 6 870eV Angle-resolved Auger spectrum X-ray: 5 fs OL: 20 fs, W/cm 2 XFEL OL Ne ++ 2p 4 Ne 1s 2 2s 2 2p 6 Interference of electron emission within one cycle of the optical laser field!!!

25 XFEL: Laser-assisted resonant Auger decay LCLS_2009 Ne + 1s -1 2s 2 2p 6 870eV X-ray: 950 ev, 2 fs OL : 800nm, 30fs Ne 1s - photoline ΔT TOF XFEL OL Ne ++ 2p 4 Ne 1s 2 2s 2 2p 6 Ne 1s Auger line ΔT TOF

26 Two-color experiments Intense XUV field: Multi-photon Ionization

27 FLASH: Non-linear Processes Ion spectroscopy in strong FEL fields λ(fel) = 13.3 nm Sorokin, Bobashev, Feigl, Tiedke, Wabnitz, Richter, Phys. Rev. Lett (2007) FEL : 93 ev, focus 2.6 μm ----> 7.8 x W / cm > Xe + Xe 21 IP(Xe 21+) 5 kev

28 Electron Spectroscopy on atomic Xe hν (FEL) 93.3 ev ; W / cm 2 One-photon Process Costello, Düsterer, Meyer, Richter et al. Two-photon Process FEL Int. Xe (focus) residual (focus) out of focus 4d Auger Xe + 4d 9 5s 2 5p 6 2 D 5/2 = 67.5 ev 2 D 3/2 = 69.5 ev

29 Electron Spectroscopy on atomic Xe hν (FEL) 93.3 ev ; W / cm 2 Intensity dependence Costello, Düsterer, Meyer, Richter et al. Two-photon Process Xe (focus) residual (focus) out of focus

30 Electron Spectroscopy on atomic Xe hν (FEL) 93.3 ev ; W / cm 2 2 x hν (FEL) 93.3 ev Costello, Düsterer, Meyer, Richter et al. Two-photon Process Xe (focus) residual (focus) out of focus 4d Xe + 4d Xe 4p Auger

31 Two-photon one-color excitation : Kr* 3d 9 4d 4d 92.0eV Kr + 3d 92 D 5/2 One-photon ionization: Kr + hν Kr + 4p 5 / 4s 1 Two-photon ionization: Kr + 2 hν Kr + 4p 5 / 4p 4 4d Auger 4p 5 hν = 46 ev 46eV Kr + 4p 4 4d 4p 4 4d 4p 5 46eV Kr + 4s 1 4p 6 Kr + 4p 5 4s / Kr+ x 1000 Kr 3d 10 4s 2 4p 6 5 μm; >10 14 W/cm 2

32 Resonant Auger Decay: Kr* 3d9 4d S. Fritzsche, P. Lambropoulos, A. Mihelic, Kr** 3d94s24p64d (J=0,2) Intensity (arb.units) Kr+ 4p44d ---> Kr+ 3d104s24p44d + e4p5

33 Two-color experiments Dissociation dynamics of H 2

34 Dissociation Dynamics in H 2 < 100 fs FEL : 13.7 nm, 90.5 ev Opt.Las. : 800 nm, 1.55 ev 400 nm, 3.1 ev hν VUV hν opt H + + H + H + + H(nl) H + + H(1s) H(1s) + H(1s) H*(n=2) : E(bind) = 3.4 ev H*(n=3) : E(bind) = 1.5 ev H*(n=4) : E(bind) = 0.8 ev E (kin.) < 1.5 ev

35 Photoionization of excited atomic fragments Energy (ev) nm H * (n) 400nm H + n=4 n=3 n=2 800nm n=3 n=4 400nm n=3 n=2 n=4 n=2

36 Ultra-fast molecular dissociation 800 nm Laser 400 nm Laser exp. fit risetime = 500 fs n=3? n=2 Fast fragmentation < 100 fs

37 Summary - Above threshold ionization (ATI) of rare gases - Beyond Soft-Photon Approximation - Non-linear (multi-photon) processes - Auger dynamics in dressed atoms (2-colour) - Ionization mechanisms (1-colour) - Resonant two-photon excitation - 1-colour vs. 2-colour - Molecular dissociation dynamics - Excitation of core resonances FLASH LCLS XFEL

38 Atomic Photoionization Dynamics in Intense Radiation Fields Experiment - LIXAM (Orsay, France) D. Cubaynes, M. Meyer - DESY (Hamburg, Germany) S. Düsterer, W.-B. Li, A. Azima, P. Radcliffe, H. Redlin, J. Feldhaus - Dublin City University (Dublin, Ireland) J. Dardis, P. Hayden, P. Hough, M. Kelly, V. Richardson, E.T. Kennedy, J.T. Costello - LCP-MR (Paris, France) R. Taïeb, A. Maquet - State University Moscow (Russia) E.V. Gryzlova, S.I. Strakhova, A.N. Grum-Grzhimailo - FORTH (Heraklion, Crete) P. Lambropoulos - Jozef Stefan Institute (Ljubljana, Slov.) A. Mihelic Theory - GSI (Darmstadt, Ger.) / Univ. Oulu (Finl.) S. Fritzsche Institute of Nuclear Physics, MSU, Moscow, November 17, 2009

39 Photoexcitation of excited molecules F. Guimaraes, F. Gel mukhanov, H. Agren et al. (KTH, Stockholm) E 1s -1 * NO* (O 1s -1 *) Theory Core-excited resonance XUV Vibrational excitation IR (intense,fs) r(a-b)

40 Vibrational wavepackets F. Guimaraes, F.Gel mukhanov et al. Phys. Rev. A72, (2005) Pump: laser Probe: FEL OL: 2 x W/cm 2, 100fs X-ray: 5 fs

41 Two-Color Pump-Probe Studies FEL Atoms Opt. laser VUV XUV - photoionization - core electrons Short fs pulses Intense pulses Molecules Model systems - electron correlation - electron/nuclear dynamics Basic processes Fundamental laws UV/Vis/NIR nm < 100 fs 1-5 mj < W/cm 2

42 FLASH (Free electron LASer in Hamburg) Ackermann et al., Nature Photonics 1, 336 (2007) RF-gun Diagnostics Accelerating Structures Collimator Undulators Laser Bunch Compressor Bunch Compressor 5 MeV 127 MeV 450 MeV 1000 MeV 300 m Bypass FEL Diagnostics LINAC : 1 GeV 30 m fixed-gap undulator macro-bunch at 10 Hz > 30 bunches, 1 μs separation log (power) 6-60 nm exponential ( gain ev) low gain (high-gain linear regime) ΔT = fs P(z) = P o exp(z/l gain ) ~ photons/pulse non-linear ~ μj (> W/cm 2 ) saturation length ~ 10 L gain gain ~ 10 5

43 FLASH + Optical Laser linac e - FEL bending magnet FEL to user electrons visible synchrotron radiation Ti:Saph laser : 800 nm 120 fs, μj -->(120 fs - 4 ps, 2 mj) CCD image Nd:YLF pump laser : 523 nm 12 ps, 600 μj TTF clock from injector rack 300 m long cables synchroscan streak camera slow feedback goal: drift < ps / h opt. laser to user Long term stability : 800 fs r.m.s Max-Born-Institut, Berlin I. Will, H. Redlin

44 ATI : Strong NIR Dressing Field (Ne) FEL: 26.9nm (46 ev) Laser: 800nm, 1.8mJ, 100fs 3x10 13 W/cm 2 Soft-Photon Approximation 5x10 11 W/cm 2 He Peak intensity Ne 2p -1 Peak height 2x10 12 W/cm Photoelectron energy (ev) Multi-photon processes A. Maquet, R. Taieb, J. Mod. Opt. 54, 1847 (2007)

45 XFEL : Dynamics of Innershell Resonances Ar 2p 3d 2p - nl Cs 3d - f Ba Arp et al., JPB32 (1999) M. Martins et al. JPB 39, 2006

46 Next: Laser-assisted Auger decay 250e V PES in strong field Ar + 2p -1 Schins et al. PRA 52, 1272 (1995) L 23 M 23 M 23 Ar 2+ Auger in strong field Ar 2p 6 3s 2 3p 6 Nov LCLS : Ne 1s at hν > 870 ev

47 Next: Laser-assisted Auger decay 250e V PES in strong field Ar + 2p -1 L 23 M 23 M 23 Ar 2+ Auger in strong field Dynamics in strong fields - angular distribution - ΔT(XUV) Γ(Nat) - resonant Auger - coupling of ionic states - control of decay Ar 2p 6 3s 2 3p 6 Nov LCLS : Ne 1s at hν > 870 ev

48 Strong XUV + NIR Fields Sequential Two-Photon Double-Ionization FEL: 46 ev, 20 μj, 30fs OL: 800nm, 1.8mJ, 3ps Energy (ev) SB S D 2 Ne 2+ 2p eV 3 P 0,1, Ne + 2p Ne 2p 6

49 Photoionization of dressed ionic states 10 Two-photon resonances 3 P 0,1,2 Intensity (arb. units) SB 1 D 2 SB SB 1 S 0 1 D 2 Ne 2+ 2p 4 Ne +* 2p 5 nl Photoelectron energy (ev) 3 P 0,1,2 I( 1 D 2 ) / I( 3 P 0,1,2 ) = 0.67 XUV

50 Self-Amplified Spontaneous Emission Cavity FEL SASE FEL Reflector Reflector Undulator e - log (power) low gain exponential gain (high-gain linear regime) P(z) = P o exp(z/l gain ) non-linear gain ~ for X-ray wavelength no efficient reflectors exist lasing in a single-pass amplified spontaneous emission saturation length ~ 10 L gain duration, length

51 Two-color experiments Two-photon resonant excitation

52 Next: Photodissociation dynamics Innershell pump-probe experiment N T N C O N N O + N C N T T I() Giffiths et al., J.Phys.B24, 4187 (1991) Binding energy (ev) U. Hergenhahn, J.Phys.B37, R89 (2004)

53 Two-photon resonance : Kr* 3d 9 4d 4d 5p 92.0eV 1.5 ev XUV 90.5eV Kr + 3d 92 D 5/2 Auger Kr + 4p 4 4d Intensity (arb. units) Resonant Auger Spectrum (Two-Photon) FEL+las FEL 3p 4 4d? 4s 4p SB Kr 3d 10 4s 2 4p 6 tof (ns)

54 Two-photon resonance : Kr* 3d 9 4d P. Lambropoulos, A. Mihelic 4d 5p 92.0eV 1.5 ev Kr + 3d 92 D 5/2 S = f(ir) Auger ΔE (ev) 5.00 Ponderomotive shift S of resonance positions 1x10 14 W/cm 2 XUV 90.5eV Kr + 4p 4 4d x10 13 W/cm 2 1x10 12 W/cm 2 Kr 3d 10 4s 2 4p Laser wavelength (nm)

55 Two-photon resonance : Kr* 3d 9 4d Kr + 3d 92 D 5/2 4d 5p 92.0eV 1.5 ev Auger 46eV Kr + 4p 4 4d XUV 90.5eV 46eV Kr 3d 10 4s 2 4p 6

56 Next: Laser-Coupling of Autoionization States He Δt ionization probability W/cm 2 δ a / Γ a Theory ionization probability W/cm 2 δ a / Γ a W/cm 2 5x1012 W/cm 2 P. Lambropoulos et al. δ a / Γ a δ a / Γ a S.I. Themelis, P. Lambropoulos, M. Meyer J. Phys. B 37, 2832 (2004) Time-dependent calculations Dynamics of electronic relaxation

57 Temporal resolution / Synchronization Average Mode: Cross Correlation Curve Single Shot Mode: Photoelectron spectra FWHM = 600 ± 70 fs T FEL =20fs T O.L. =120fs 0 ps temporal resolution T = 600 fs Jitter (FEL) = 550 ± 80 fs temporal resolution T 50 fs only for overlapping pulses M. Meyer et al. PRA R (2006), P. Radcliffe, et al., APL (2007) A. Maquet, R. Taïeb, J. Mod. Opt (2007)