Abstract
We have studied the concentration dependent fluorescence decay kinetics of ceramic Nd:YAG, to resolve inconsistencies in the previous literature. Our data indicate that earlier reports of single exponential lifetimes even at Nd concentrations of a few percent were due to the effects of long-pulse excitation. Under short-pulse excitation the fluorescence decay is nonexponential for concentrations greater than about 1% atomic. Energy migration to sinks consisting of cross-relaxing Nd ions dominates at long times, whereas single-step energy transfer to randomly distributed quenching sites dominates at earlier times. The concentration dependence of this single-step transfer indicates direct cross-relaxation between individual ions at concentrations below 4% atomic, but resonant transfer to quenching sites consisting of Nd pairs at higher concentrations.
Highlights
Dramatic improvements in transparency in recent years have made ceramic laser materials such as Nd-doped YAG very promising competitors for the customary single-crystal laser gain media [1, 2]
The quadratic concentration dependence of the migration transfer rate inferred from the exponential tail of the decay curve is consistent with quenching by cross relaxation between Nd ions, but does make clear whether the quenching occurs primarily within closelyspaced pairs, or whether pairs at many spacings contribute substantially
The complex concentration dependence of the rate parameter for this transfer is best explained by assuming that transfer to two-ion quenching centers dominates at high concentrations, but that direct cross-relaxation between isolated ions dominates for concentrations below about 4%
Summary
Dramatic improvements in transparency in recent years have made ceramic laser materials such as Nd-doped YAG (yttrium aluminum garnet, Y3Al5O12,) very promising competitors for the customary single-crystal laser gain media [1, 2]. It is important that this difference in decay kinetics be clarified, since laser application of highly concentrated ceramic Nd:YAG requires knowledge of the energy storage time, and since 807 nm is essentially the same as the most commonly used diode pump wavelength for Nd:YAG lasers. Another uncertainty regarding concentration quenching in Nd:YAG arises from recent studies of relatively low-concentration single-crystal samples. We report here the results of concentration quenching studies on Konoshima Nd:YAG ceramic samples with concentrations in the range 0.09% to 9% atomic. Disagreements noted above, and highlight complications that arise due to inhomogeneities in highly concentrated samples
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