Ultraintense light matter studies with a Compact Laser System

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Ultra-intense light matter studies with a Compact
Laser System

• Enam Chowdhury, Barry Walker,Chad Materniak, Joe
  Yang(?), Dan Dakin(?)
• University of Delaware

I. Laser System II. Physics of Ultra-intense
Field Ionization IV. Experimental Observations
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• Laser Specs (figure, beam profile, focussing
  ability, Photograph of laser system etc.)
• Experimental setup (chamber, pulser etc. may be a
  figure, Spectra)
• Analysis of High field ionization aspects,
• a. Ionization from bound states (Wave function
  calculation etc.)
• b. Continuum dynamics (Electrons path
  deflected due to magnetic field
• and possible effect in
  non-sequential ionization)
• Experimental DATA
• Future aspects (look ionization at higher fields,
  Radiation from accelerated electrons in laser
  focus, etc.)

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Motivations

• Understand basic ultraintense field/atomic
  physics
• Atomic response is the first step to analyze
  novel relativistic and non-linear effects, such
  as electron correlation, effect of the magnetic
  field of the laser
• Insight into related high field phenomena,
  e.g. short pulse X-rays, electrons, protons,
  and ions in the keV to MeV range

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Experimental Laser System

• A compact CPA laser system that can operate at 9
  Watts with 6 mJ pulses at 3 kHz
• OR
• 5 tera-Watts with 300 mJ pulses at 10 Hz
• AND
• The whole setup fits into a 12 x 4 optical Table

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Laser Specifications

• 25?5 fs width
• 1.2 ?0.06 J energy
• 10 Hz repetition rate, linearly polarized, 800
  nm.
• Focused spatial profileFWHM diameter 3?0.4 ?m
• Pulse duration energy focal spot
  measurements, estimated peak intensity 1020
  W/cm2 per joule of energy

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Experimental Ion Apparatus

• Laser is focussed by a big f/2.5 metal off-axis
  parabolic mirror
• Ionizes 200 mm gas jet He, Ne, Ar
• Ions analyzed by a 1 m TOF spectrometer

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Time of Flight Ion Spectrum
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Experiment and Theory Comparison
Compare the measured charge state distribution to
calculated ADK charge state distribution
Keldysh parameter, ? 0.03ltlt1 implies,
ionization by tunneling.
Plot the deviation between experiment (1.5 1019
W/cm2 ) vs. ADK yields (1.5?1 1019 W/cm2)
Best fit occurs for 0.6 1019 W/cm2
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Experiment Vs. Theory Analysis

• ADK formulation adequate for Ar9 - Ar14
• An order of magnitude deviation at Ar16 data
• At fields 100 a.u. is... Non-relativistic
  ADK model valid ???

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Two-Step Strong Field Model
I) Ionization II) Continuum and Recollision
Dynamics
??? Relativisitic or Non-Relativistic ???
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Step One ADK Ionization Analysis
?0 gtgt 1/Z
Wave function Quasi-classical
Electron ionizes by tunneling through the
AtomLaser field barrier along the ? r - z
co-ordinate
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r01a.u.
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Ar15
So, even at Relativistic fields, ionization
can be treated in a non-relativistic,
semi-classical way.
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Relativistic Considerations

• Step 1 Ionization
• Relativistic modification to bound state wave
  function O((Z?)2) 1
• The Forgotten Magnetic ForceAr15 bound state
  electron velocity Zc?/n 6 of c. Therefore,
  v/c ? B is significant ... deviations from ADK
  model likely
• Step 2. Continuum Electron
• Electron energies in ponderomotive potential 0.1
  to 1 MeV
• Electron dynamics is relativistic BUT
  nonrelativistic in vicinity of potential where
  ionization occurs.
• Immediate vicinity of the barrier, acceleration
  of electron is slow

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Future Experiments

• Addition of a potential sift in flight tube, to
  isolate single high charge states.
• Numerically solve Schrodingers equation to
  compare to ADK
• New Laser system
• 9.4 Watt kHz Regenerative Amplifier
• TW amplifierbeing installed this week

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Conclusion

• Ionization of high charged states of Argon have
  been observed. Relative yield of the ions have
  been analyzed at laser intensity of 1.5?1?1019
  W/cm2
• Measured ion yields for Ar9 to Ar14 fit the
  non-relativistic ADK tunnel ionization model
• Ar16 needs detailed probing to identify
  possiblerelativistic ionization effects

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Laser Specifications

• 1.2 ?0.06 J energy
• 25?5 fs width
• 10 Hz repetition rate, linearly polarized, 800
  nm.
• The pulse is compressed temporally in a
  high-vacuum
• The spatial profile of the attenuated pulse at
  the focus is measured. FWHM diameter 3?0.4 ?m
• dominant focal aberration is chromatic, reducing
  energy at the focus by a factor of 2
• Pulse duration energy focal spot
  measurements, estimated peak intensity 1020
  W/cm2 per joule of energy

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OUTLINE
1 minute - Intro 1 slide, motivation 1 slide 2.5
minutes - Laser Specs 5 minutes - Physical
Analysis 2 minutes - Data 1 minute - future 1
slide 0.5 minutes - conclusion - 1 slide