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strong-field physics in the x-ray regime

strong-field physics in the x-ray regime. Louis DiMauro ITAMP FEL workshop June 21, 2006. fundamental studies of intense laser-atom interactions generation and application of attosecond pulses ultra-fast optical engineering. LCLS parameters.

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strong-field physics in the x-ray regime

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  1. strong-field physics in the x-ray regime Louis DiMauro ITAMP FEL workshop June 21, 2006 • fundamental studies of intense laser-atom interactions • generation and application of attosecond pulses • ultra-fast optical engineering

  2. LCLS parameters • XFELs are an x-ray source of unprecedented brightness • only viable sources are accelerator-based

  3. undulator B-field w ~ cm g e- SASE FEL • lasing builds up from noise LCLS is great but not perfect

  4. …and welcome to the 70’s! …so theorists beware what we think we are measuring may not be what we are measuring!

  5. Linac Coherent Light Source at SLAC • 15 GeV e-beam, 100 meter long undulator • output: 0.8-8 keV (1.5 A), 10 GW, 1012 photons/shot, 230 fs, 120 Hz • five thrust areas slated for first operations

  6. LCLS experimental halls AMOP at the LCLS • AMOS team located in the near-hall • initial experimental end-station on soft x-ray beamline (0.8-2 keV) • scientific thrust: fundamental strong-field interactions at short wavelengths

  7. AMOS team experimental menu • short term strategy • shine light on Roger’s wall (scientific impact) • define a prominent role in XFEL development • atomic ionization (nonlinear physics/metrology) • x-ray scattering from aligned molecules (laser/x-ray experiments) • cluster dynamics (non-periodic imaging)

  8. contrast: long and short wavelength strong-field physics ponderomotive potential is everything at long wavelengths e- in Coulomb + laser fields • electron ponderomotive energy (au): • Up = I/42 • displacement:  = E/2 • PW/cm2 titanium sapphire laser: Up ~ 60 eV &  ~ 50 au for LCLS @ 102 PW/cm2 Up &  are zero!

  9. laser multiphoton ionization neon photoabsorption n=2 • x-ray multiphoton ionization contrast: long and short wavelength strong-field physics • laser multiphoton ionization n=1

  10. photoionization correlated ionization Auger sequential 2-photon, 2-electron x-ray strong field experiment x-ray multiphoton ionization

  11. reaction microscopy Schmidt-Böcking needle in the haystack: coincidence measurements • detect by correlating particle-particle events J. Ullrich et al., JPB 30, 2917 (1997)

  12. coincidence measurement true-to-false ratio: T/F =  t C f (1 C + N1)(2 C +N2) t,1,2(,,)  detection coefficients N1,2 noise counts C  average count rate f  repetition rate • the 120 Hz operation of the LCLS makes coincidence experiments high risk, thus the initial AMOS end-station will not have this capability.

  13. AMOS end-station: single-shot measurements courtesy of John Bozek

  14. LCLS parameters for strong-field studies photon energy: 800 eV number of photons: 1013/shot pulse energy: 1 mJ peak power: 5 GW focused spot size: 1 m flux: 1033 cm-2 s-1 intensity: 1017 W/cm2 period: 2 as number of cycles: 40,000 ponderomotive energy: 25 meV displacement: 0.003 au

  15. optical frequency tunneling frequency   = (Ip/2Up)1/2-1 lcls       excimer MPI Ti:sap & Nd mir CO2 tunnel MPI “photon description” “dc-tunneling picture” tunnel   • data compiled based on both electron and ion experiments global survey of single atom response Keldysh picture

  16. neon photoabsorption L-shell photoionization K-shell 1-photon, 1-electron ionization consider a 1-photon K-shell transition: K  10-18 cm2 RK = KFlcls  1015 s-1 (saturated) tK = 1/RK = 1 fs • rapid enough to ionize more than one electron! • fast enough to compete with atomic relaxation? • is the external field defining a new time-scale?

  17. neon KK 10-52 cm4 s 2-photon, 2-electron 2-photon, 2-electron ionization consider a 2-photon KK-shell transition: KK  10-49 cm4 s RKK = KKF2lcls  1017 s-1 (saturated) tKK  10 as • so RKK  RK S.A. Novikov & A. N. Hopersky, JPB 35, L339 (2002)

  18. i.e. is it sequential ionization? photoionization Auger photoionization 2-photon, 2-electron 2-photon, 2-electron ionization • are the electrons correlated? • in a strong optical field single electron dynamics dominate.

  19. 2-photon, 1-electron ionization • consider a 2-photon K-shell transition: • estimate 2-photon cross-section, 2perturbative scaling laws1: 2 10-54 cm4 s2nd-order perturbation theory2: 2  10-52 cm4 s transition probability: P2 = 2F2lcls 0.1-1 1P. Lambropoulos and X. Tang, J. Opt. Soc. Am. B 4, 821 (1987) 2S. A. Novikov and A. N. Hopersky, JPB 33, 2287 (2000)

  20. bound-c-c ATI distinguishable bound-continuum ATI Auger ATI x-ray above-threshold ionization • estimate (2+1)-photon cross-section, 2+12+1 = 2cycle 10-90 cm6 s2P2+1 = 2+1F3 lcls  10-4 • ATI should be observable

  21. lcls II MPI tunnel MPI tunnel   can the LCLS get to the strong-field regime • impose a Keldysh parameter of one   = (Ip/2Up)1/2  Up  400 eV (8 eV)@ 800 eV, intensity needed is 1021 W/cm2(1014 W/cm2) = 0.3 au (19 au) • number of photons is fixed, require tighter focus and shorter pulselcls ~ 10 fs (very possible)thus require a beam waist of 50 nm (in principle possible)

  22. Cornell Energy Recovery Linac there are other sources on the horizon 107 photons/shot in 20 fs repetition rate: 0.1-1 MHz

  23. coincidence measurement true-to-false ratio: T/F =  t C f (1 C + N1)(2 C +N2) t,1,2(,,)  detection coefficients N1,2 noise counts C  average count rate f  repetition rate • the 120 Hz operation of the LCLS makes coincidence experiments high risk, thus the initial AMOS end-station will not have this capability. • the ERL does have the advantage of high duty cycle! • does it have high enough intensity for exploring multiphoton processes?

  24. maybe? • consider a 2-photon K-shell transition: • estimate 2-photon cross-section, 2perturbative scaling laws1: 2 10-54 cm4 s2nd-order perturbation theory2: 2  10-52 cm4 s ERL parameters: 106/shot, 100 fs, 1A 20 nm waist yields flux ~1030 cm-2 s-1 (1015 W/cm2) transition probability: P2 10-(57) 1P. Lambropoulos and X. Tang, J. Opt. Soc. Am. B 4, 821 (1987) 2S. A. Novikov and A. N. Hopersky, JPB 33, 2287 (2000)

  25. LCLS ERL two-photon ionization • use near resonant enhancement of 2 • increase number of photons/shot over average power open the possibility of temporal metrology!

  26. neon KK 10-52 cm4 s 2-photon, 2-electron 2-photon, 2-electron ionization consider a 2-photon KK-shell transition: KK  10-48 cm4 s PKK  0.1 • coincidence investigations: • atomic • aligned molecules • cluster dynamics S.A. Novikov & A. N. Hopersky, JPB 35, L339 (2002)

  27.   1012 W/cm2 Auger laser 1012 W/cm2 Auger electron ~ 200 eV M M Auger incoherent x-rays (250-400 eV) L L photoionization x-ray-laser metrology

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