OPTICALLY INDUCED 2-PHONON PROCESSES CONNECTING THE E-BAR(2E) STATES IN RUBY

The population ratio N-N+ of the Zeeman states of Ē(E2) has been measured over five decades of metastable-state concentrations N- in 2500-ppm ruby at 28 kG and 1.5 K, i.e., in the absence of thermalization between Ē±. Upon raising the pumping, N-N+ falls below the value corresponding to optical feeding only due to optically induced two-phonon processes via 2Ā(E2). Rate equations account for the findings under the assumption of marginal (ballistic regime) or moderate (spatially diffusive regime) trapping of these 29-cm-1 phonons. At high pumping, N-N+ further drops to unity, reflecting disturbance of the Boltzmann equilibrium within the A24 ground state. © 1979 The American Physical Society.