Polarization-spectroscopy measurement of the homogeneous linewidth of an inhomogeneously broadened color-center band

A polarized laser beam can bleach narrow, long-lived, anisotropic holes in the 607-nm zero-phonon line of the NaF $N_1$ center. The width of these holes is twice the homogeneous linewidth, and three orders of magnitude less than the inhomogeneous width of the line. We report a polarization-spectroscopy technique which detects the dichroism and birefringence of the hole with better sensitivity than absorption spectroscopy. A simple rateequation model is developed to account for hole burning, but the recovery of the initial isotropic absorption profile appears to be a complex, slow, and intractable process.