Optical Homogeneous Linewidths and Spectral Diffusion at 1.5 microns in Mixed Er$^{3+}$:Eu$^{3+}$:Y$_{2}$SiO$_{5}$ Studied by Photon Echo

Er$^{3+}$-doped materials are important for spectral hole burning applications at 1.5 micron communication wavelengths, including analog signal processing and laser frequency stabilization. Doping Er$^{3+}$:Y$_{2}$SiO$_{5}$ with Eu$^{3+}$ is shown to broaden the inhomogeneous linewidth of the $^{4}$I$_ {15/2}$ - $^{4}$I$_{13/2}$ transition without significantly broadening the homogeneous linewidth. This maximizes bandwidth in real-time analog signal processing applications without compromising resolution. Photon echo and stimulated photon echo decays between 1.5 K and 5.5 K were measured along with angle- dependent Zeeman spectra and site-selective absorption and emission. Detailed modeling of observed spectral diffusion induced by spin dynamics considered Er$^{3+}$-Er$^{3+}$ dipole interactions driven by direct-phonon processes. The model describes and explains observed behavior and predicts behavior vs. magnetic field, crystal temperature, Er$^{3+}$ dopant concentration, and crystal orientation. $^{*}$ Currently at University of San Francisco $^{**}$ Currently at University of South Dakota