Frequency-domain measurement of spontaneous emission lifetime in rare-earth-doped gain media

The spontaneous emission lifetime in Al2O3:Tm³⁺ waveguides is measured to be 568 ± 48 μs, using a frequency-domain method. The method is studied and verified in Er³⁺-doped silica fiber, yielding a measured lifetime of 9.73 ± 0.08 ms.