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Upconversion and reduced ^4F_3/2 upper-state lifetime in intensely pumped Nd:YLF

1999; Optica Publishing Group; Volume: 38; Issue: 12 Linguagem: Inglês

10.1364/ao.38.002714

0003-6935

J. D. Zuegel, W. Seka,

Luminescence Properties of Advanced Materials

Nonexponential decay of the 4F3/2 upper laser state in Nd:YLF was observed with time-resolved fluorescence spectroscopy and small-signal gain probes in low-doped (1.16-at. %) samples when intensely pumped to high population inversions. A rapid initial decay is observed after Q-switched laser pumping, followed by a longer nonexponential decay that is clearly identified as a phase of migration-assisted energy-transfer upconversion (ETU) in the hopping regime. During this phase, a rate-equation treatment is valid and the macroscopic ETU coefficient, α2 = (0.98 ± 0.03) × 10-16 cm3/s, is directly evaluated from the decay kinetics. The ETU and the migration microparameters are also estimated to be Cda* ≈ 200 × 10-40 cm6/s and Cdd ≈ 1000 × 10-40 cm6/s, respectively, and are compared with theoretical values found in the literature. On the basis of these values, rate-equation treatments of intensely pumped Nd:YLF are not strictly valid.