Optical properties of shock-compressed diamond up to 550 GPa

A series of shock wave experiments were conducted to measure the optical properties of single-crystal diamond $\ensuremath{\langle}100\ensuremath{\rangle}$ in the pressure regime between 60 and 550 GPa. The results show that the transparency limit of diamond at 532 nm is $\ensuremath{\sim}170\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. When the applied pressure in diamond is lower than its Hugoniot elastic limit (HEL), diamond remains transparent during both compression and release processes. At the pressures between the HEL and the limit of its transparency, however, diamond is found to be transparent only while the compression is maintained and gradually loses its transparency during the subsequent release process. We also found that the refractive index of single-crystal diamond \ensuremath{\langle}100\ensuremath{\rangle} monotonically increases as density increases to the limit of its transparency, in contrast to the previous static reports on continuous decrease of refractive index with increasing pressure up to 40 GPa.