Effects of Superhyperfine Interactions on Photon-Echo Behavior in Dilute Ruby

A detailed analysis of the photon-echo decay in dilute ruby is presented. The experimental results are in quantitative agreement with an echo-decay theory based on the magnetic interaction between the Cr electronic spin and neighboring Al nuclear magnetic moments. Specifically, the following photon-echo properties are explained by the Cr-Al interaction: (i) modulation of the echo as a function of pulse separation time, (ii) the rapid decay of the echo from the ⁴A(mₛ=3/2) to ²E(mₛ=1/2) transition, (iii) the dependence of the echo on the direction and magnitude of an external magnetic field, (iv) the echo behavior at the 2.06- and 4.12-kG level crossings, and (v) the photon-echo decay in low magnetic fields. In addition, the experiments presented here show that the Cr-Al magnetic interactions in the ²E excited state are roughly the same as the corresponding interactions in the ⁴A₂ ground state. The relationship of the photon-echo results to recent fluorescence-linewidth measurements is discussed.