Accumulated photon echo in ruby under hydrostatic pressure: Ground-state splitting and spontaneous decay of 2A¯(2E)

The technique of accumulated photon echo is used in combination with a high-pressure diamond anvil cell to measure the splitting of the $^{4}$${\mathit{A}}_{2}$ ground state and the one-phonon spontaneous decay rate of the 2A\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E) level at 1.5 K in ruby up to 4.3 GPa of hydrostatic pressure. The $^{4}$${\mathit{A}}_{2}$ ground-state splitting is found to be 0.383\ifmmode\pm\else\textpm\fi{}0.001 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at ambient pressure, and increases with a slope of +(6\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$/GPa. The spontaneous decay rate of 2A\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E) increases only weakly with pressure. The pressure dependences of both quantities are accounted for in terms of the trigonal-field and spin-orbit-coupling parameters.