Homogeneous broadening and hyperfine structure of optical transitions in ${\mathrm{Pr}}^{3+}$:${\mathrm{Y}}_2$${\mathrm{SiO}}_5$

Contributions to the homogeneous linewidth of the ${}_{}{}^3{}_{}{}^{}$${\mathit{H}}_4$(1)${\to }^1$${\mathit{D}}_2$(1) transition for the two crystallographic sites of ${\mathrm{Pr}}^{3+}$ in ${\mathrm{Y}}_2$${\mathrm{SiO}}_5$ have been investigated using photon echoes. The effects of excitation-intensity-dependent dephasing or instantaneous diffusion were systematically studied to allow accurate determination of the optical resonance widths. Homogeneous linewidths of 2.8 kHz (site 1) and 1 kHz (site 2) were measured with no applied magnetic field and with sufficiently low laser intensity to minimize the effects of instantaneous diffusion. Using the same excitation intensity, widths of 2.1 kHz (site 1) and 0.85 kHz (site 2) were obtained with an applied magnetic field of 77 G, demonstrating a significant contribution of ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ nuclear-spin fluctuations to the zero-field homogeneous linewidth. Extrapolation to zero excitation intensity yielded optical resonance widths that were only slightly narrower than the measured values. Optically detected nuclear magnetic resonance measurements determined the hyperfine structure of the ${}_{}{}^3{}_{}{}^{}$${\mathit{H}}_4$ ground state for each site; the hyperfine levels of the lowest component of the ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$ manifold for each site were determined using photon echo nuclear double resonance. The relatively large oscillator strength of 3×${10}^{\mathrm{-}7}$ for a rare-earth ion, in conjunction with long dephasing times makes this material a useful candidate for demonstration of time-domain signal processing and optical data storage.