Advanced Accelerator Concepts, Austin, TX, June 15, 2012
Single-Shot Tomographic Imaging of
Evolving, Light Speed Object
Zhengyan Li, Rafal Zgadzaj, Xiaoming Wang, Yen-Yu Chang,
Michael C. Downer
Department of Physics and Institute of Fusion Studies
The University of Texas at Austin, Austin, TX 78712
Evolution of index structures is common in different medium and
different applications…
Simulation of evolving wakes for e- self-injection in LWFA
S. Kalmykov, et al., PRL 103, 135004 (2009)
Simulation of evolving electron driving and witness
beam in electron-driven plasma accelerators
I. Blumenfeld, et al., Nature 445, 741-744 (2007)
Simulation of evolving pulse intensity during nonlinear propagation in fused silica
A. Couairon, et al., Phys. Rev. B 71, 125435 (2005)
Single-shot visualization in laboratory of evolving refractive index structures!
Single-shot Frequency-Domain Holography (FDH) took snapshots
of quasi-static laser wakefields…
N. Matlis et al., “Snapshots of laser wakefields,” Nature Physics 2, 749-753 (2006)
Phase accumulated in the collinear
probe averages the z-dependence of
the wakefields, i.e. index structure
η(r, ζ, z). Thus FDH can only take
snapshots of quasi-static objects.
As a generalization FDH, Frequency-Domain Streak Camera (FDSC)
is a time sequence of the object’s tomographic projections…
Z. Li, et al., “Frequency-domain streak camera for ultrafast imaging of evolving, light-speed objects,” Opt. Lett. 35, 4087-4089 (2010)
FDSC is a time sequence of the object’s
projections along projection angle ϕ
𝜙 = arg
1
𝑣𝑝𝑟
𝑣𝑝𝑟
1−
cos 𝜃 + 𝑖
sin 𝜃
𝑣𝑜𝑏
𝑣𝑜𝑏
𝑣𝑜𝑏
Frequency-domain tomography (FDT) incorporate multiple
probes to get FDSC covering projection angles from -70 to 70
degree in a single shot…
Compact probe array generation are based on nonlinear optical
effects for tomographic application…
BBO
Go to another
HZF4 for chirp
Large n2 glass HZF4
for cascaded FWM
 No movable parts for
tomographic angle scanning
 Self-synchronized by imaging the
“sandwich” to interaction region
400 nm probes
through SHG &
SFG: 15 in total
Incident
beam pair
polarization
800 nm cascade
FWM: 8 in total
 Up to 15 probes generated with
comparable energy
 Minimized phase mismatch in
BBO by using correct polarization
 Compact and inexpensive
Frequency domain streak cameras (FDSC) coded in selected 5 probes
Angular or temporal multiplexing of probes enables cost-efficient
data collection with a single spectrometer in a single shot…
FDH raw data
Probe 1
Ref
Probe 1
Ref
Probe 2
Probe 1
Probe 2
Probe 3
Ref
2D Fourier transform
Single-shot tomographic movies reveal dynamics of nonlinear
pulse propagation, i.e. self-focusing, laser filamentation, plasma
generation…
Simulation of femtosecond pulse nonlinear propagation is consistent
with measured movie, including effects of diffraction, dispersion,
self-focusing, plasma effect, and multi-photon processes…
400 nJ
500 nJ
600 nJ
700 nJ
What interesting physics can we learn from movies for glass experiments?
It is not only a prototype experiment for future application in plasma based wake field
accelerators, but also important to understanding femtosecond filamentation.
Lightening control
White-light LIDAR
J. Kasparian et al., Science 301,61-64 (2003)
Nature Photonics 3, 120 - 121 (2009)
Triggering rain in air
P. Rohwetter et al., Nature Photonics 4,
451 - 456 (2010)
What is the mechanism of filamentation?
Established theory: the balance
between positive nonlinear
V. S.
refractive index n2I and negative
index by plasma
A. Couairona, et al., Phys. Rep. 441, 47-189 (2007)
P. Polynkin, et al., PRL 106, 153902 (2011)
J. M. Brown, et al., Opt. Lett. 37, 1604-1606 (2012)
New theory: negative contribution of
high order nonlinearity (e.g. n4, n8)
leads to saturation of nonlinear
refractive index
P. Bejot, et al., PRL 104, 103902 (2010)
P. Bejot, et al., PRL 106, 243902 (2011)
C. Bree, et al., PRL 106, 183902 (2011)
Different mechanisms yield different behaviors of refractive
index profiles…
Established theory
New theory
For peak plasma density, i.e. steady state
Movie frame at z = 2.5
mm for 700 nJ pump
In simulation, plasma effect starts to balance
nonlinear Kerr effect at z = 2.5 mm, with laser
peak intensity of 26 TW, and plasma density of
~1018 cm-3
Our “movie” supported the established theory about plasma effect for glass in our parameter regime.
Single-shot tomographic technique, i.e. frequency-domain
tomography (FDT), yields a movie of wake-field evolution or electron
bunch interactions for both high and low density LWFA/PWFA…
Index structure evolution in laserfilamentation in glass medium
A broadening of probe bandwidth to ~100 nm for
temporal resolution of ~10 fs
For high density LWFA,
modified FDT system
with broader bandwidth
can make a movie of
wake-field “bubble”
evolution
For low density LWFA/PWFA, small oblique angle probing reveals temporal profile evolution
For LWFA @ Texas
Petawatt, temporal
profile of wake field
and its elongation and
contraction would be
visualized, which is
critical for electron
injection.
Summary
• Frequency-domain tomography (FDT) applies multiple probes at
different angles in a single shot, yielding a movie of evolving index
structures.
•
FDT is compact and inexpensive by generating multi-probe array
through standard nonlinear optical effects, and by detecting probes
through angular/temporal multiplexing methods.
• The application of FDT to laser-dielectrics interactions reveals the
mechanism of femtosecond filamentation.
• FDT will be applied to wake field diagnosis in future.
This work is supported by U.S. Department of Energy (DoE) grants DE-FG02-07ER54945
and DE-FG02-96ER40 954 and National Science Foundation (NSF) grant PHY-0936283