presented by emily sprague pulse institute, aaron lindenberg, dan daranciang, & haidan wen
DESCRIPTION
Created by mode-locked oscillators ▪ Ti:sapphire oscillators ▪ wavelengths of 680 nm to 1130 nm Optimization ▪ Minimal chirp ▪ Large bandwidth Used to generate plasmaTRANSCRIPT
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Bi-plasma interactions on femtosecond time-scalesPresented by Emily SpraguePULSE Institute, Aaron Lindenberg, Dan Daranciang, & Haidan Wen
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Overview Background
▪ Plasma Filamentation▪ THz generation
Experimental Setup
Results
Conclusions
Future WorkCourtesy of http://en.wikipedia.org/wiki/Plasma_%28physics%29
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Ultrafast pulses are on the order of the femtosecond (10 − 15 second)
Created by mode-locked oscillators ▪ Ti:sapphire oscillators▪ wavelengths of 680 nm to
1130 nm
Optimization▪ Minimal chirp▪ Large bandwidth
Used to generate plasma
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Plasma is formed through a process called photoionization
Photons from an external source are absorbed by a gas, emitting electrons
Because of abundance of charge carriers, interacts with itself and surrounding EM fields
Used in THz generation
Courtesy of http://www.isibrno.cz/omitec/index.php?action=libs.html
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THz radiation are E&M waves with frequencies of ~ 1012 Hz
Could potentially replace x-rays as a form of non-ionizing radiation
Applications in medical imaging, material science studies, and atomic spectroscopy
5 types of plasma-based generation methods
Courtesy of http://www.stanford.edu/group/lindenberg/research.html
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AC-bias method produces a transverse polarization without use of electrodes
Superposition of fundamental and second-harmonic pulse fields
Optimization▪ Relative phase
shift▪ Exact temporal
overlap▪ Polarization
Courtesy of M.D. Thomson, M. Kreß, T. Loffler, and H.G. Roskos. Laser & Photon. Rev. 1, No. 4, 349–368 (2007)
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Studying multiple plasmas could lead to production of more efficient THz radiation
Ti:sapphire laser▪ 50 fs 800 nm pulse
Mirrors Lenses
▪ f=100 mm (beam 2)▪ f=200 mm (beam 1)
Beam splitter▪ Controls polarization
beam 1: p-polarized beam 2: s-polarized
Delay Stage▪ Controls path length and
relative delay between arrival of plasmas
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Polarization studies s-p polarized
▪ Beam 2 vertically polarized▪ Beam 1 horizontally
polarized
s-s polarized▪ Beam 1 and beam 2
vertically polarized
p-p polarized▪ Beam 1 and beam 2
horizontally polarized
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Time delay studies
Before time-zero: no plasma interaction
Time zero: both plasmas arrive and interfere
After time-zero: secondary fluorescence
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Camera images (from above) of bi-plasma overlap
Time Zero: two plasmas arrive simultaneously
Before time zero
After time zero
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Origin of dramatic enhancement at time zero is not understood
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Results (cont’d)
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Trends
200 250 300 350 400 4500
100200300400500600700
P-P Polarized
Delay Arm Power (mW)
Inte
nsity
Rat
io
250 300 350 400 450 500 550 60005
101520253035
S-S Polarized
Delay Arm Power (mW)
Inte
nsity
Rat
io
250 300 350 400 450 5000
100200300400500600700
S-P Polarized
Delay Arm Power (mW)
Inte
nsity
Rat
io
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Conclusions Peak intensity and point of decay consistently occured
at the same time values
Decay time was constant across all polarizations (~50 steps)
All power levels and polarization sets experienced a full decay back to the starting intensities
No valuable data was obtained below a power of 250 mW
Peak intensity was always strongest for s-p polarizations and weakest for p-p polarizations
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Conclusions (cont’d)
Slope of the decay decreased with decreasing power in stationary arm
Peak and decay ratios increased with decreasing power in the stationary arm
Results are reproducible
Spike at time zero is dramatic and still not understood by scientific community
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Future Work Time dependent
spectral studies of plasma
▪ Analysis of wavelengths of plasma fluorescence
▪ Resolve between scatter or enhanced tunneling ionzation
Better camera resolution
Courtesy of http://opticsclub.engineering.ucdavis.edu/
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Thank you!