Transcript Development of Shock Diagnostics at the Z

Douglas Allen Dalton
Will Grigsby
Aaron Bernstein
Despina Milathianaki
Todd Ditmire
Eric Taleff
Jonathan Brewer
Richard Adams
Patrick Rambo
Larry Ruggles
Ian Smith
John Porter
Development of Experiment for Materials
Studies at the Z-Beamlet Laser Facility
WB
W4
W_unwrapped2
for i  0  300
VPF0 
2 (1   )

c
Reflecting
Anti-Reflecting
Mirror
Reflectivity/Interferometry
Probe
By putting the image plane at the output
beamsplitter, adjustments optimizing
fringe contrast are decoupled from
adjustments optimizing fringe orientation
and fringe spacing.
When the pump beam hits the target,
ablation of the material into vacuum
initiates a shock wave that propagates
toward the back surface.
Compression
Wave
P  0U S U P

 U S / (U S  U P )
0
Anti-Reflecting
Mirror
Reflecting
Image Plane
Injection to Fiber
Shock Velocity: US
Particle Velocity: UP
Pressure: P
Density: ρ
Initial Density: ρ0
Bulk Sound Speed: c0
Constant: a
1 Shock Breakout
Uneven
4.5
4
3.5
3
2.5
Velocity
0 j 2
1.5
1
0.5
0
0
To Streak
Camera
6
8 10 12 14 16 18 20
~5x1012 W/cm2, giving a maximum pressure of 1.4 Mbar and maximum density of 1.7 ρ0.
The equation of state used was: US=5.386 um/ns + 1.339UP
Fiber
Lasers enable us to determine the material
strength at higher strain rates.
3” Mirror
Periscope
Key Design Features
•Fast Optics
•Optical Fiber
•Mach-Zehnder interferometer
10 cm f.l. achromat
50/50 Beamsplitter
Rarefaction wave from reflection
of shock from back surface
•Spall is the planar separation of material
due to tensile stress, which is induced by
crossing rarefaction waves. The spall
pressure and strain rate can be found from
an interferogram.
1
Pspall 
2
0 c(umax  umin )
u 1
 

 t 2c
Streak Camera
2 ns
Spall
No spall signal
CCD Camera
•Through Fresnel’s Reflectivity equation, material conductivity can be found.
4 /   1  2(2 /  ) 2
R
1
4 /   1  2(2 /  ) 2
Position
2D short pulse diagnostics give an advantage of
looking at the shock breakout at a point in time.
Z-Beamlet is a Nd:Glass laser with
a multi-pass amplifier design.
Reflectivity Image
Position Interferogram
Result from
non-uniform
beam
SEM image showing the back
surface of a spall target.
Time
•The 2D interferometer gives the interface/free surface displacement at a
snapshot in time.
•Mapping out position versus time, the interface/free surface velocity
can be determined.
Rarefaction wave from
decrease of drive pulse
7.5 mm
1
Line-VISAR and 2D Reflectivity/Interferometry
are being fielded at Z-Beamlet to test Aluminum.
4
ps_px

j
1000
Interferogram and maximum velocity profile for 50 micron Aluminum on
LiF impacted at
We are using the Z-Beamlet Laser to drive shock waves.
Energy: 1.2 kJ at 527 nm
Pulse Length: 1-1.8 ns
Beam Profile: Square and Top-Hat
Spot Size for Experiments:
2 mm-10 mm
2
Time
Incoming Light
Particle velocity is determined with VISAR and 2D Interferometry. Using the
Equation of State of a material, we can establish shock velocity, pressure, and
compression.
22 
Time (ns)
15 cm f.l. achromat
U S  c0  a  U P
Etalon
Beamsplitters
To Camera
Ablation
1
W5i  k
2 ns
W5
1
4h(n  )(1   )
n
Velocity  VPF0  Phase
VISAR Probe
Pump beam

W4
W5i  k
Velocity (microns/ns)
(100) Lithium
Fluoride (Melt)
An advantage to using Z-Beamlet is that we can reach pressures necessary to
for
W4
600 1over2a large
melt
aluminum
area. (In order to drive a 1D shock, the ratio of laser
W4i k k  150

k target
1 thickness must be ≥ 3:1)
spot sizei to
1.79 mm
50 um Aluminum (Melt)
350 um Aluminum (Spall)
The VISAR (Velocity Interferometer System for Any Reflector) measures a Doppler shift
in the probe light. By using a streak camera, we can image a line from the target. This
gives both spatial and temporal information. Upon retrieving the phase out of an
interferogram, the velocity is found by multiplying the phase by the velocity per fringe
constant.
for
0  600 1
Shock loading with lasers enables
W5 t WB
us to study material melting.
for i k0 FindDiscontinuityTime

600
1
if
FindDiscontinuityTime
0
for
 300
it
it
1.79 mm
The shock experiments that we perform at Z-Beamlet are pump-probe style experiments.
The Line-VISAR measures the material velocity.WPhase
Position
Lasers enable us to study the state of materials and the
dynamics of material processes.
Interferogram of a 350 micron free standing
target impacted at ~7x1011 W/cm2.
Mirror
Half-wave plate
A pulse stacker is needed so
that we can look at a larger time
window over which the spallation
process occurs.
Polarizing
Beamsplitter
Mirror
Half-wave plate
3 mm
3 mm
Further developments are needed to make future progress.
VISAR probe beam:
532 nm, 8 ns FWHM, ~5 mJ
Reflectivity/Interferometry probe beam:
1054 nm, 500 fs, ~10 mJ
Nearly complete loss of
light in shocked region
Although this is not the data that we expected, we can redesign the system for a
faster collection optic. We previously used ~f/16 collection optic, but now want an f/3 optic.
•Build pulse stacker for events that occur on a longer time scale.
•Continue developing other short pulse techniques.
•Implement use of a phase plate to produce more uniform shocks.