Excited-State Absorption and Photoconductivity of GSGG:Cr and GSAG:Cr

Abstract

The garnets Gd₃Sc₂(GaO₄)₃ (GSGG) and Gd₃Sc₂(AlO₄)₃ (GSAG) have been shown to be promising host materials for tunable, near-infrared lasers when doped with Cr³⁺ [1], and to be the most efficient, flashlamp-pumped Nd³⁺ laser active media when codoped with Cr³⁺ and Nd³⁺ [2]. Both of these notable successes have as their origin vibronically broadened electronic transitions between ligand field states of the Cr³⁺ ion which are responsible for its excellent sensitizer and tunable laser properties. In addition to these transitions associated with the ground state, there is a set of excited state absorption (ESA) transitions associated with the Cr³⁺ fluorescent level which must be understood in order to fully model the performance of both types of lasers. Recently, the ESA spectra of GSGG:Cr and GSAG:Cr were measured [3] and shown to consist principally of two forbidden ligand field transitions at 9,000 and 19,400 cm⁻¹ and an electric dipole-allowed transition (σ ~ 10⁻¹⁷ cm²) at 32,000 cm⁻¹.