Ultraslow Optical Dephasing of LaF3:Pr3+

Optical free-induction dephasing times as long as 16 μsec, corresponding to an optical homogenous linewidth of 10 kHz, have been observed for the ${}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}\leftrightarrow {}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ transition of ${\mathrm{Pr}}^{3+}$ ions in La${\mathrm{F}}_3$ at 2°K. Measurements are facilitated by a frequency-locked cw dye laser and a new form of laser frequency switching. Zeeman studies reveal a Pr-F dipole-dipole dephasing mechanism where the Pr nuclear moment is enhanced in both ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}$.