Diamond anvil Raman gauge in multimegabar pressure range

The first-order Raman band of diamond anvils has been investigated at pressure up to 380 GPa in order to develop an optical pressure determination method. The high frequency edge of the band was calibrated by the pressure scale of the equation of state of Pt. The universality of the relationship between the sample pressure and the edge-frequency was confirmed up to 370 GPa and the usefulness of the diamond anvil Raman gauge was demonstrated. Using the diamond anvil Raman spectroscopy, the stress-state of the anvil culet was directly observed in the multimegabar pressure range. Obtained pressure dependence of the shear stress suggested further extension of feasible pressure beyond 400 GPa.