Physical Review Letters
Ultrahigh-Resolution Spectroscopy: Photon Echoes in YAl O3 : Pr3+ and La F3 : Pr3+
R. M. Macfarlane, Robert M. Shelby, R. L. Shoemaker
Abstract
By using a new, delayed-heterodyne photon-echo technique, we have obtained a spectral resolving power of 1.2\ifmmode\times\else\texttimes\fi{}${10}^{11}$, measuring a 2.0-kHz linewidth (half width at half maximum) for the 6105-\AA{} $^{1}D_{2}\ensuremath{\leftrightarrow}^{3}H_{4}$ transition of YAl${\mathrm{O}}_{3}$: ${\mathrm{Pr}}^{3+}$ in an external magnetic field. This appears to be the highest resolution ever obtained in optical spectroscopy. Measurements were also made on the corresponding transition of La${\mathrm{F}}_{3}$: ${\mathrm{Pr}}^{3+}$ giving a linewidth of 5 kHz. Optical free induction decay gave incorrect results (i.e., significantly broader linewidths).