Gated IR images of shocked surfaces. Page: 3 of 5
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TABLE 1. Physical Characteristics of Tin Targets and Camera Gate Times; to is Shock Breakout Time
Camera open and close gate times relative
Step to shock breakout (us)
Height Thin Step Thick Step Flat
# Geometry Surface Finish (mm) (openclose) (open,close) (openclose)
1 Step Machine finish (#8) 1.0 t4O40, t0+540 to-230, t+270
2 Flat Polished w/3 pm A1203 to-230, to+270
Metal samples were prepared with three
different surfaces: single step, periodically spaced
grooves, and flat polish. Although a variety of
geometries were studied, only single step and flat
polished tin (99.9%) data are presented in this
paper. The details of sample preparation and IR
camera gate times (open and close), relative to
shock breakout, are summarized in Table 1. All
metal samples were nominally 2 mm thick and
21 mm in diameter.
Camera (SBF-134) Setup and Calibration
General performance characteristics of the
SBF-134 are summarized in Table 2. A detailed
temperature calibration was performed using a
blackbody source placed in the explosive chamber
at the target position. However, for this publication
radiance data was not temperature converted. We
intend to present temperature calibrated data in a
Pressure Calibration and Timing Measurements
The pressure generated by the explosive in the
metal coupon was calculated from Hugoniot and
measured shock velocity data. The shock velocity
was obtained by measuring the time required for the
shock wave to travel across a 1 mm step, machined
in a test sample. The step was coated with a thin
(<25 pm) film sensor that produces a prompt
(<10 ns rise) burst of light when shocked. This thin
film is a mixture of cerium doped lutetium
orthosilicate (LSO:Ce) phosphor powder suspended
in a silica glass binder. An optical fiber positioned
2 mm from the sample surface simultaneously
views the high and low surfaces of the step. When
the shock arrives the sensor emits a burst of light
that is detected with a photomultiplier tube and
recorded with a transient digitizer. Using this
method, a pressure of 19.7GPa was determined for
the tin experiments.
For each gated imaging experiment, a 3-mm-
diameter spot of the previously-discussed shock
arrival sensor was applied approximately 5 mm
from the target center. Shock-induced light from
this sensor was recorded simultaneously with the
high explosive and camera triggers. Such cross
timing is essential to interpret the acquired IR
image. The jitter between the trigger used to initiate
the high explosive and the time of arrival of the
shock at the target surface was found to be on the
order of 200 ns.
Figures 2 and 3 show a set of images of samples
1 and 2 in Table 1. In each of these figures, a gated
IR image of the shocked target surface (a) is
displayed next to a white light image of the pro-
shocked sample (b) taken with a digital camera. A
"log counts" grey scale map is used to display the
14-bit digitizer range and to highlight the subtle
features in the shocked metal surface.
Figure 2 (a) shows the results from the stepped
tin. Notable features include high radiance along the
step boundary, and an offset in radiance between
the thin and thick steps. The bright circular feature
is the high-emissivity phosphor LSO:Ce sensor.
The semi-circular feature marking the outer edge of
the lower half of the coupon results fronmjotion of
the thinner step, presumably with hot gasses
escaping from around the edge.
TABLE 2. Camera Performance Characteristics
Pixel Size Quantum Efficency Bit Photons/Pixel Minu.m Gate
Detector Array Size (pim) (3-5 pm) Depth Required for 2:1 SNR Width (ns)
InSb 256 x 256 30 -85% 14 500 140
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Lutz, S. S. (Stephen S.); Turley, W. D. (William Dale); Rightley, P. M. (Paul M.) & Primas, L. E. (Lori E.). Gated IR images of shocked surfaces., article, January 1, 2001; United States. (digital.library.unt.edu/ark:/67531/metadc929127/m1/3/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.