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- F. Crim
Coherent Phase Control of Electronic Transitions in Gallium - - PowerPoint PPT Presentation
Coherent Phase Control of Electronic Transitions in Gallium - - PowerPoint PPT Presentation
Coherent Phase Control of Electronic Transitions in Gallium Arsenide Robert J. Gordon, Sima Singha, and Zhan Hu Department of Chemistry University of Illinois at Chicago FRISNO 11 Aussois, France March 31, 2011 Passive Control F. Crim
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Active Control
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Outline
- Motivation and methods
- Results from open loop experiments
- Results from closed loop experiments
- Proposed mechanism
- Conclusions
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Cut in Decemet’s Membrane
6 ns, 1064 nm
30 ps, 1064 nm
Vogel, et al., Invest. Ophthalmol. Vis. Sci. 35, 3033 (1997)
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Surface Modification with Ultrafast Pulses
Stoian, et al., Appl.Phys.
- Lett. 80, 353 (2002)
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SEM images of the ablation craters on GaAs
1, 5 and 5+1 pulse trains
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Outline
- Motivation and methods
- Results from open loop experiments
- Results from closed loop experiments
- Proposed mechanism
- Conclusions
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- Phys. Rev. B 82, 115205 (2010)
LIBS/Photoluminescence Spectrum
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Effect of Laser Polarization
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PL Signal at 450.8 nm
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Control Landscape
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Effects of Polarization and Incidence Angle
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Effect of Laser Fluence
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Effect of Laser Phase
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Outline
- Motivation and methods
- Results from open loop experiments
- Results from closed loop experiments
- Proposed mechanism
- Conclusions
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Closed Loop Control
Sine phase optimized for 390-450 nm sine phase optimized for 420-440 nm random phase optimized for 390-450 nm
- J. Phy. Chem. A (in press)
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20100528-115537 PRB paper graph
Optimum Pulse Shapes for Open and Closed Loops
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Effect of Laser Fluence
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Effect of Laser Polarization on Optimized PL Spectrum
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Effect of Laser Phase on Open-Loop Spectrum
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Effect of Laser Phase on Closed-Loop Spectrum
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Outline
- Motivation and methods
- Results from open loop experiments
- Results from closed loop experiments
- Proposed mechanism
- Conclusions
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Mechanistic Questions
- Where does the new band come from?
- How is it possible to excite optical
phonons at fluences above the threshold for melting?
- How does light couple to the plasma?
- How does energy couple to the phonons?
- Where does the coherence come from?
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Ratio of double pulse to single pulse fluorescence as a function of delay time and total energy
Si<111>
- App. Phys. Lett. 90, 131910 (2007), J. Appl. Phys. 104, 113520 (2008)
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- Dispersion relation for
a light wave in a plasma:
- Critical density:
- Index of refraction:
- Total reflection:
pe L L pe L
c k ω ω ω ω ≥ ⇒ + =
2 2 2 2
2 2
4 e m n
L e cr
π ω =
2 2 2
1 1
L pe cr e
n n n ω ω ε − = − = =
θ θ ε
2 2
cos ; sin ) (
cr e
n n z = =
Light Propagation in a Plasma
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Brunel or vacuum heating
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Comparison of Closed and Open-Loop Pulses
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Conclusions
- Coherent control of carrier recombination was achieved
at fluences well above the damage threshold.
- The primary mechanism for open loop control appears to
be phonon-hole scattering, with trapping of carriers in the L-valley.
- Brunel (ponderomotive) heating launches ballistic
electrons that excite the phonons.
- Effect of laser phase suggests a competition between
photoemission and phonon excitation.
- Random phase optimization appears to converge to a
different control pathway.
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YaomingLu, Youbo Zhao, Slobodan Milasinovic John Penczak, SimaSingha, Zhan Hu
Supported by NSF, USAF Surgeon General, UIC
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( ) ( )
[ ]
ϕ π ω ψ + − = T m m A / 2 sin
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Time Delay Scans
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