Physical Review Letters
Photon Echoes below 1 K in a Nd3+ -Doped Glass Fiber
John Hegarty, Matthijs M. Broer, Brage Golding, J. R. Simpson, John B. MacChesney
Abstract
Optical dephasing rates ${{T}_{2}}^{\ensuremath{-}1}$ of a dilute concentration of ${\mathrm{Nd}}^{3+}$ ions in a pure silica fiber have been studied from 0.05 to 1.0 K with use of two-pulse photon echoes. Echoes obtained by resonant excitation of ${\mathrm{Nd}}^{3+}$ into the metastable $^{4}F_{\frac{3}{2}}$ state from the $^{4}I_{\frac{9}{2}}$ ground state have yielded ${{T}_{2}}^{\ensuremath{-}1}=1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ ${\mathrm{s}}^{\ensuremath{-}1}$ at 0.1 K which follows a ${T}^{\frac{4}{3}}$ temperature dependence to 1.0 K. A crossover of ${{T}_{2}}^{\ensuremath{-}1}$ to a ${T}^{2}$ temperature dependence above 1 K is inferred by comparison with earlier high-temperature linewidth measurements on this transition.