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 $\langle 100\rangle$ in the pressure regime between 60 and 550 GPa. The results show that the transparency limit of diamond at 532 nm is $\sim 170\mathrm{GPa}$. 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 〈100〉 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.

Figure 1

Typical experimental setup of target consisting of polypropylene, aluminum, and single-crystal diamond 〈100〉. For some shots, an antireflection coated z-cut α-quartz was also on the rear surface of aluminum next to the diamond sample as a pressure standard. The thicknesses of polypropylene, aluminum, diamond, and quartz were 15, 40, 500, and 50 μm, respectively.

Figure 2

Typical VISAR signal count profiles at three pressures. Time $\left(t\right)$ zero is set when the shock wave breaks into the diamond from the aluminum. The signal count is normalized by the count at $t=0$. The attenuation coefficient was calculated from the attenuation of the signal counts during the time, $t_e$, which is presented by a red two-direction arrow for the 62 (± 4) GPa shot.

Figure 3

VISAR measurements of apparent particle velocities from the aluminum-diamond interface through (a) purely elastic compression of diamond and (b) elastic-plastic compression of diamond. The shock front of diamond does not become reflective in our pressure range.

Figure 4

Attenuation coefficients at 532 nm versus pressure measured for shocked single-crystal diamond 〈100〉. The red and blue symbols denote the elastic and plastic regions, respectively.

Figure 5

Apparent particle velocity versus true particle velocity of single-crystal diamond 〈100〉 at 532 nm. The red and blue symbols denote the elastic and plastic regions, respectively.

Figure 6

Refractive index at 532 nm versus density of shocked single-crystal diamond 〈100〉. The symbols are the same as in Fig. 5. Black square and red triangles are the ambient value (Ref. [2]) and the data from elastic shock experiments using a gas gun (Ref. [4]), respectively.