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Femtosecond micromachining of internal voids in high explosive crystals for studies of hot spot initiation
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View: Figures


Image of FIG. 1.
FIG. 1.

Experimental setup. Spec: Kaiser Holospec spectrometer; RNF: Raman notch filter at ; SP1: short pass filter reflects ; L1: focal length achromat lens; PH:150 micrometer pinhole; LP1: long pass filter reflecting ; Cam: microscopy camera; Obj: tube length, 1.25 numerical aperture Meiji plan achromat objective with working distance; sample: transparent single crystal of explosive in immersion oil, backlit for observation.

Image of FIG. 2.
FIG. 2.

Isolated voids created at the damage threshold energy in PETN (a), RDX (b), and HMX (c) are observed with optical microscopy.

Image of FIG. 3.
FIG. 3.

The effects of laser energy on isolated void formation in PETN (a), RDX (b), and HMX (c) are visualized with optical microscopy. Numbers indicate multiples of threshold energy; the lowest measured energy producing damage. No damage occurs below 1.0.

Image of FIG. 4.
FIG. 4.

Microcracking above threshold occurs preferentially along certain crystal planes in PETN (a), RDX (b), and HMX (c). The number inset indicates the multiple of threshold energy used to create the voids.

Image of FIG. 5.
FIG. 5.

Lines are formed by consolidating voids every along one dimension in PETN (a), RDX (b), and HMX (c).

Image of FIG. 6.
FIG. 6.

Extended damage is apparent in optical micrographs of 5 and diameter three-dimensional spheres created from consolidating single voids spaced at in every dimension. In-plane damage is in focus, while out of plane damage appears blurred. PETN (a), RDX (b), and HMX (c).

Image of FIG. 7.
FIG. 7.

Optical micrographs of diameter spheres in PETN (a), RDX (b), and HMX (c). Confocal Raman images over nearly the same area as (a)–(c) showing the intensity of the Raman peak at in PETN (d), in RDX (e), and in HMX (f). Full Raman spectra were recorded at every step. Images shown have been median filtered for clarity. While a specific Raman peak is used for each material, images plotted at any Raman frequency exhibit the same spatial structure.

Image of FIG. 8.
FIG. 8.

Confocal Raman spectra recorded in pristine regions (offset by ), the damage regions shown in Fig. 7 (offset by ), and the difference spectra (offset by ). The difference spectra would show negative features if chemical products were present, but no negative features are observed. Only a loss of intensity is seen in PETN (a), RDX (b), and HMX (c), establishing that the defects created are low density voids.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Femtosecond micromachining of internal voids in high explosive crystals for studies of hot spot initiation