Nonlinear absorption in a Cr4+ : Gd2SiO5 crystal subjected to picosecond excitation

The optical absorption, temperature dependences of the luminescence intensity and decay time, and the transient absorption spectra of a Cr⁴⁺ : Gd₂SiO₅ crystal were determined by the picosecond excitation and probing method. An analysis of the results showed that the induced absorption observed in the 600–650 nm range was due to ³T₂(³F) → ³T₁(³P) transitions from the excited state. The lifetimes of the ³T₂(³F) and ³T₁(³F) levels were estimated to be 15 ns and 12 ps, respectively. The cross section for absorption from the first excited state at the wavelength of 616 nm was (1.1 ± 0.6)×10^-18 cm² and that for absorption from the ground state at λ = 540 nm was (2.2 ± 1.1)×10^-18 cm².