Effects of Nearly Degenerate States on Photon-Echo Behavior

Abstract

A density-matrix analysis is given of some properties of photon echoes arising from nearly degenerate ground and/or excited states. Modulations of the echo intensity as a function of pulse separation time are predicted as well as more complicated effects near level crossings. In particular, the analysis is applied to the 2.06-kG level crossing in the ground state of ruby.