Composite picture depicting the optical configuration used in ps-CARS temperature measurements following laser flash heating of energetic nanomaterial samples. A ns-duration flash-heating laser impinges on the sample from above; three incoming ps-duration CARS beams overlap at a point above the sample surface (along the z-axis dimension), producing a fourth outgoing CARS signal beam. Pictorial overlays within the image include an example shadowgraph of a shock wave and an example reacting-plume Mie-scattering image to provide reference.
Shock-wave evolution following laser flash heating of samples containing 50-nm aluminum nanoparticles embedded in ammonium nitrate. Full-frame image height is 105 mm.
(a) Time-dependent shock-wave position, r, depicted as symbols for four aluminum nanoparticle samples; curves correspond to power-law least-squares fits. (b) Corresponding calculated time-dependent energy release for the four denoted aluminum nanoparticle samples. (c) Comparison of energy released, normalized for mass fraction of aluminum in each sample. In (b) and (c), symbols are connected by line segments for clarity.
Example single-shot N2 ps-CARS spectrum following flash heating of sample containing 50-nm aluminum nanoparticles. The included theoretical spectrum was calculated using the modified Sandia CARSFT code with an assumed temperature of 3600 K.
Spatially resolved ps-CARS temperatures measured for 50-nm nanoparticle samples shown with respect to a measured shadowgraph image. All depicted measurements were made at a delay of 1.3 μs after flash heating. At this delay, the shock-wave radius is 2.33 mm, and the three temperature measurements correspond to heights of z = 1.25, 1.5, and 1.75 above the sample surface.
Comparison of observed ps-CARS (symbols) and theoretical (curve) temperatures for samples containing 50-nm nanoparticles at several distances, z, above the sample at a delay of 1.3 μs after flash heating. Theoretical temperature is determined based on the measured shock-wave position as a function of time.
Temperature at reaction-plume front observed for four aluminum-nanoparticle samples.
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