Ruby at high pressure. III. A pumping scheme for the R lines up to 230 GPa

We report on a B-line pumping scheme for exciting ruby R-line fluorescence which becomes useful above ∼100 GPa (100 GPa=1 Mbar). We have measured five ruby fluorescence lines in a quasihydrostatic-hydrogen-pressure medium to 230 GPa by using the most efficient argon-ion pump-laser wavelength at each pressure. The frequencies of the R and R′ lines, as determined in the cubic-crystal-field approximation, shift linearly with the fractional volume change to the highest pressure reached. The ${\mathrm{R}}_1$ and ${\mathrm{R}}_3^{\prime }$ lines remain thermalized and the oscillator strength of the ${\mathrm{R}}_3^{\prime }$ line increases relative to the ${\mathrm{R}}_1$ line to 230 GPa.