Knowledge Bank

Divalent vanadium substituted into weak field fiuoride crystals is an example of a phonon-terminated four-level laser with the emission terminating on vibrationally excited levels of the ground electronic state. Laser action in vanadium-doped magnesium fluoride ($MgF2:V+2$) at a wavelength of $1.12\mu m(8915cm+1$) was reported by johnson $etal1$ as early as 1966. In an extensive experimental study of the optical properties of $MgF2:V+2$, Moulton $etal2$ discovered an unfavorably strong excited-state-absorption (ESA) transition which overlapped the $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}T2\to 4A2$ laser transition. We have carried out configuration interaction electronic structure calculations on the ground and excited states of $MgF2:V+2$ in order to better understand the nature of the ground and excited state absorption. These theoretical studies represent the most accurate ab initio calculation of the optical spectrum of an ion/host system to date. The calculated position of the zero phonon line corresponding to the origin of the $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}T2(B2)$ absorption band was found to be in error by only 2.3%. Similar accuracy was obtained for the peak of the $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}A2\to 4T2$ absorption. As determined from the calculated potential energy curves, the predicted peak of the $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}T2\to 4A2$ emission at $9195cm-1$ is in error by only $-275cm-1(3\%)$, which is consistent with the magnitude of the agreement for the zero-phonon line, but opposite in sign. The energies for the ESA transitions from the $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}T2(B2)$ state to the crystal field split components of the $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}T1a$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}T1b$ excited states have been calculated and will be discussed.