Ultraslow optical dephasing inEu3+:Y2SiO5

Abstract

We report the measurement of what we believe to be the narrowest known optical resonance in a solid. This was made on the $^{7}$${\mathit{F}}_{0}$${\ensuremath{\rightarrow}}^{5}$${\mathit{D}}_{0}$ transition of ${\mathrm{Eu}}^{3+}$:${\mathrm{Y}}_{2}$${\mathrm{SiO}}_{5}$ at 1.4 K using photon echoes with sufficiently low laser power to almost eliminate contributions from instantaneous diffusion. The optical resonance widths measured for ${\mathrm{Eu}}^{3+}$ ions in the two crystallographic sites of ${\mathrm{Y}}_{2}$${\mathrm{SiO}}_{5}$ and in a magnetic field of 100 G are 122 Hz (site 1) and 167 Hz (site 2). These widths are dominated by population decay, but up to 20 Hz is attributed to $^{89}\mathrm{Y}$ spin fluctuations which have been reduced by the applied magnetic field.