PHYSICAL CONSEQUENCE:

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semi-classical rescattering

• PHYSICAL CONSEQUENCE
• electron capture results in odd harmonic
  photons.
• harmonic cutoff (3Up IP) rule !!
• elastic scattering yields energetic (10Up)
  electrons.
• inelastic e-2e scattering ? multiple electron
  ejection.

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• tunnel (vo0)v(t) Eo/?cos?t - cos?o
• backscatter (? ?)set v(?r) -v(?r)
• v(t gt tr) Eo/?(cos?t - cos?r) (cos?r -
  cos?o)

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Semi-classical solution of generalized
SFA Lewenstein et al., PRA 51, 1495 (1995)

• backscattering results in production of high
  energy electrons

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helium, 0.8 ?m, 0.8 PW/cm2
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helium, 0.8 ?m
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Up ? ip2
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• some insights into double ionization
• NS linked to depletion of the neutral ground
  state.
• first electron tunnels into the continuum.
• the NS yield is strongly polarization dependent
  as compared to the sequential processes.

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• Experiment performed at two intensities.
• 0.8 PW/cm2 1/500
• 0.4 PW/cm2 1/1000
• 3He is used for coincidence measurement.

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• mechanical referencing design
• common interaction volume
• pulsed mode operation
• dual MCP detection
• UHV environment (10-10 t)

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mass spectrometer
electron spectrometer
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• an 81 XeKr gas mix test was used to test the
  coincidence apparatus.

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205M shots 45M He hits 1058 He2 coin
81014 W/cm2

• double ionization results in hotter
  distribution than single ionization.
• distribution consistent with e-2e rescattering.

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helium, 0.4 ?m

• reduce ponderomotive energy by 4 since Up ? ?2

• The double-to-single ionization ratio is equal
  for 800 nm 400 nm excitation.

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is the Keldysh picture relevant for multiple
ionization?
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ratio double-to-single ionization

• non-sequential ionization exists for all inert
  gases in the near-ir.

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? ?
Chaloupka et al. PRL 90, 33002-1 (2003).
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• rescattering model captures the essential
  physics
• single electron approximation
• quasi-static limit
• tunneling regime

• experimental test of the model has been limited
• starting to understand many-body effects
• little or no experiments
• relativistic regime
• long wavelength regime
• strong-field short wavelength limit

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scaling laws suggest that wavelength is important
parameter for altering the intense laser-atom
interaction.

• SF wavelength scaling parameters
• Keldysh adiabaticity parameter ?????-1
• ponderomotive energy Up???2
• wave packet spread ???

• the scaling of the physics is virtually untested.
• may provide a new paradigm in the physics.

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inert gas
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• you can really see these harmonics!

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low frequency limit ??? 1

• Large ponderomotive energy
• Up ? ? ?2
• Access tunnel ionization in more atoms
• ??????atom
• Paradigm for laser-atom interaction
• test scaling laws
• accessible to control schemes
• simplify metrology

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• ponderomotive or quiver energy Up ?2 ? /4
• displacement ? ? 2 E

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high frequency limit ?????atom ??gtgt 1 SF limit
?o ? 1 au
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• fel oscillators are well established facilities.
• operate from the far-IR visible.
• high average power performance.
• limited by optics.

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1.5-15 A, 1012/pulse, 200 fs, 120
Hz commissioning 2007-08
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Five experiments slated for first operationssee
2000 BESAC report LCLS The first
experimentsat www.er.doe.gov/production/bes/BESA
C/pubs.html.
target studies atomic physics femotchemistry nano
scale dynamics in condensed phase plasma warm
dense matter structural studies on single
biomolecules
Real answer No one knows?
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xenon at 770 nm and 790 nm
Rudati et al. PRL 92, 203001-1 (2004).
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Isolated Core Excitation Gallagher Cooke (1978)
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Rydberg

• transient Rydberg population is shelved, while
  the core electron is excited.
• the differential shift between Rydberg doubly
  excited states is near zero.
• unlike ICE, the Rydberg electron is not a simple
  spectator in FIRE.
• scheme of Charalambidis et al. holds at low
  intensity, Up ?? ?E PRA 50, R2822 (1994).