Sub-kilohertz optical linewidths of the ⁷F₀ ↔ ⁵D₀ transition in Y₂O₃:Eu³⁺

Homogeneous optical linewidths as small as 760 Hz (fwhm) have been observed in Y2O3+ using delayed heterodyne photon echoes. Hyperfine and lifetime contributions to dephasing are estimated to contribute {slanted equal to or less-than} 300 Hz to this width, and the remainder is attributed to quasi-resonant energy transfer. © 1981.