Nd:YAG at its 50th anniversary: Still to learn

The paper presents a critical review of the actual knowledge on Nd:YAG and brings new data on the spectroscopic properties and energy transfer self-quenching processes and on their implication in laser emission. - Highlights: • No evidence of defects such as the "dead sites" or large-scale site inversion was found. • Nd³⁺ and Y³⁺ antisite random distribution cause multicenter structure and non-exponential decay. • Down-conversion and up-conversion are permanently competing self-quenching processes. • The thermal field during lasing does not follow necessarily the absorbed pump distribution. • Direct pumping in the emitting level enhances the laser performances and power scaling.