| Research Abstract |
Metastable phases of diamond, amorphous and nanocrystalline diamond, were produced by SCARQ (shock compression and rapid quenching) method based on the shock-gun technology, This method was also applied to a laser-shock technology, which was developed in this study. Two-types of laser-shock method were investigated ; one was the direct use of laser-induced ablation pressures, and the other was the use of the laser-driven flyer impact, For the latter, thin aluminum foils were accelerated by a high power Nd : YAG pulse laser and impacted PMMA window placed at a certain distance. Arrival time of the flyers was detected by a streak camera. Spatial changes in the arrival time revealed the curved flyer shape depending on the laser energy distribution which resulted in velocity distribution. Moreover, these profiles were strongly dependent on the distance from focal point of laser. Therefore, it was difficult to reduce the focal spot size less than 0.1 mm whose value was required for achieving the diamond transition pressure of 50 GPa. These experimental data were described by computer simulation based on one-dimensional hydro-code.
The structural change of fullerene films subjected to laser-shock compression using the laser was investigated by Raman scattering. Some samples transformed into fullerene polymer, and the photo-induced structural change of fullerene was also investigated.
An infrared radiometer for the accurate measurement of shock temperature was developed in order to investigate shock-induced, dynamic reaction processes of materials. To determine the IR-radiometer, the shock temperature measurements of carbon tetrachloride were conducted below 10 GPa, and the results confirmed that the system was available to measure relatively moderate shock temperatures lower than 1000 K.However, the system might be available at higher temperature in the case of laser-shock because of the small shock-compressed area.
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