Photon-gated spectral hole burning in ${\mathrm{LiGa}}_5$${\mathrm{O}}_8$:${\mathrm{Co}}^{2+}$

Photon-gated hole burning, or selective bleaching enabled by a second light source, has been observed in ${\mathrm{Co}}^{2+}$ in tetrahedral sites of ${\mathrm{LiGa}}_5$ ${\mathrm{O}}_8$. This leads to long-lived spectral holes with a width of ∼1 GHz at 1.6 K. It is proposed that two-step photoionization of ${\mathrm{Co}}^{2+}$ is responsible for the hole burning. Much narrower (∼40 MHz) transient holes and antiholes were burned using population storage in nuclear hyperfine levels. These two mechanisms of hole burning are reported here for transition-metal ions for what is believed to be the first time.