研究目的
To validate the LASEM technique for potential implementation at Los Alamos National Laboratory (LANL) by acquiring early-time data to better constrain the characteristic laser-induced shock velocity model for a range of HE materials of interest.
研究成果
Ultra-high-speed shadowgraphy was implemented to characterize the air shock wave generated by laser ablation of HE materials and provide ultra-high fidelity early-time data necessary for validation of the LASEM technique. The results obtained did not support the published characteristic laser-induced shock wave velocities that provided differentiation between HE materials, but rather demonstrated that the temporal shock wave velocity history profiles were indistinguishable from one another for eight different HE materials of interest.
研究不足
The laser irradiance (peak power) implemented differed from that used in published LASEM literature, which influences the formation of the material plasma by laser ablation, and by extension, the air shock wave velocity. The overall velocities of the laser-induced air shock wave velocities generated in the present study may have decayed to the speed of sound faster than those published.
1：Experimental Design and Method Selection:
The experiment replicated the essential aspects of LASEM, using inline-focused shadowgraphy paired with an ultra-high-speed framing camera to characterize the shock wave generated by laser ablation of HE material for times ranging from 0–12 μs.
2：Sample Selection and Data Sources:
Targets were prepared using glass microscope slides, double-sided adhesive, and a spatula for spreading of the HE material. HE targets included RDX, DAAF, NONA, TNT, and compositions C4, Comp B, Cyclotol, and Octol.
3：List of Experimental Equipment and Materials:
A 12-ns full-width-at-half-maximum pulse from an Nd:YAG laser operating at 1064 nm was employed to ablate the HE target materials. The laser was focused onto each HE target via a turning mirror and a 100-mm focal-length, plano-convex lens. The inline-focused shadowgraph system consisted of collimating, focusing, and imaging lenses for a 640-nm spoiled-coherence laser illumination source.
4：Experimental Procedures and Operational Workflow:
The target slides were oriented parallel to the optics table and mounted to a three-axis translational stage to permit laser ablation across the entire HE sample. A total of 20 shots were fired for each HE tested by translating the stage in 2.5-mm increments in the x- and y-axes.
5：5-mm increments in the x- and y-axes.
Data Analysis Methods:
5. Data Analysis Methods: Laser-induced air shock images were analyzed to determine the outermost radial shock location in each frame. A user-monitored, automated image processing routine implemented in MATLAB was deployed for data analysis.
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