Measurement of the relaxation time τ21 of a Y3Al5O12:Nd3+ crystal

The relaxation time of the transition from the lower laser level ⁴I_11/2 to the ground state ⁴I_9/2 of the Nd³⁺ ions was determined experimentally for a crystal of Y₃Al₅O₁₂:Nd³⁺. The relaxation time was measured by two independent methods. The value obtained, τ₂₁≤3·10^–7 sec, was associated with the very broad (up to ~ 900 cm^–1) phonon spectrum of the garnet crystal.