High-efficiency photochemical hole burning for an infrared color center

The photochemical hole-burning properties of the 8892-A\r{} zero-phonon-line defect absorption in electron-irradiated NaF:${\mathrm{OH}}^{\mathrm{\ensuremath{-}}}$ and NaF:${\mathrm{Mn}}^{2+}$ at liquid-helium temperatures are described and analyzed. This system is the first reported example of high-efficiency (${10}^{\mathrm{\ensuremath{-}}2}$) hole burning for a color center in alkali halides. Although the width of the inhomogeneously broadened line increases linearly as the ${\mathrm{OH}}^{\mathrm{\ensuremath{-}}}$ concentration is varied by a factor of 25, the hole width extrapolated to zero burning power remains essentially constant at 1.65\ifmmode\pm\else\textpm\fi{}0.15 GHz over the same range. In contrast to most other color centers, holes can be burned 100% deep in this system, which suggests the absence of strong reverse reactions. A kinetic model for hole-growth data is presented that includes the effects of the homogeneous line shape and the dependence of the density of centers and burning flux upon distance into the sample. The hole-growth dynamics follow first-order kinetics quite well over two decades in time indicating that the quantum efficiency is essentially constant for all centers. This is evidence that the hole-burning process involves electron tunneling over a well-defined single barrier.