Transient excited-state absorption measurements in chromium-doped forsterite

The nonradiative transition dynamics between the excited ${}^3{A}^{″}{[}^3{E(}^3{T}_{1a}\left)\right]$ state and the metastable ${}^3{A}^{″}{[}^3{E(}^3{T}_2\left)\right]$ storage state of the tetravalent chromium ion $\left({\mathrm{Cr}}^{4+}\right)$ in forsterite is investigated using femtosecond excite-and-probe technique. Following excitation to ${}^3{T}_{1a}$ with pump pulses at 750 or 773 nm the induced excited state absorption was probed with femtosecond pulses in the ultraviolet (306 nm), visible (650 nm), and infrared (1500 nm). The nonradiative decay time from ${}^3{T}_{1a}$ to ${}^3{T}_2$ was estimated from the rise time of the excited state absorption at 1500 nm using a rate equations model and its value at room temperature is only 3±1 ps.