We have measured the fluorescence quantum efficiency in Ti3+:sapphire single crystals between 150 K and 550 K. Using literature-given effective fluorescence lifetime temperature dependence, we show that the zero temperature radiative lifetime is (4.44 ± 0.04) μs, compared to the 3.85 μs of the fluorescence lifetime. Fluorescence lifetime thermal shortening resolves into two parallel effects: radiative lifetime shortening, and non-radiative transition rate enhancement. The first is due to thermally enhanced occupation of a ΔE = 1,700 cm−1 higher (top) electronic state of the upper multiplet, exhibiting a transition oscillator strength of f = 0.62, compared to only 0.013 of the bottom electronic state of the same multiplet. The non-radiative rate relates to multi-phonon decay transitions stimulated by the thermal phonon occupation. Thermal enhancement of the configuration potential anharmonicity is also observed. An empiric expression for the figure-of-anharmonicity temperature dependence is given as (T) = (0)(1 + β exp(−ℏωco /kBT )), where (0) = 0.276, β = 5.2, ℏωco = 908 cm−1, and kB is the Boltzmann constant.
We present a generally applicable theoretical model describing excited-state decay lifetime analysis of metal ions in a host crystal matrix. In contrast to common practice, we include multi-phonon non-radiative transitions competitively to the radiative one. We have applied our theory to Co ions in a mixed AgClBr crystal, and as opposed to a previous analysis, find excellent agreement between theory and experiment over the entire measured temperature range. The fit predicts a zero absolute temperature radiative lifetime τrad(0) = 5.5 ms, more than three times longer than the measured effective low-temperature one τeff(0) = 1.48 ms. Furthermore, the fit configuration potential dissociation energy has been estimated as D = 2500 cm and the lattice vibrational cutoff frequency as ħωco = 180 cm. We have experimentally verified the latter by optical reflection measurement in the far-IR.
We present the implementation of Co2+:MgAl2O4 transparent ceramics as passive Q-switching elements in an Er:Glass laser at 1.534 µm. Linearly polarized pulsed output was obtained by Brewster angle inclination of the material Q-switching plate relative to the laser axis. Separate pulses were ∼105 ns long (FWHM), exhibiting ∼6.2 kW peak power at near TEM00 quality. Several fundamental sample properties important for laser intracavity operation were measured; thermo-optic coefficient dn/dT = ( − 3.8 ± 1) × 10−5 °C−1, thermal lensing factor L−1d(nL)/dT = 2.59 × 10−5 °C−1, linear expansion coefficient α = (3.9 ± 0.6) × 10−5 °C−1, polarizability thermal coefficient ϕ = (7.2 ± 2.2) × 10−5 °C−1, and damage threshold ∼6.5 J/cm2.
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