A model to account for the defects generated by ion irradiation in the electronic loss regime, and based on non-radiative decay of selftrapped excitons, is discussed and compared to experiments. It takes into account the competing role of the light-emission (radiative) and defect-creation (non-radiative) decay channels. Calculations are applied to LiNbO 3 , a useful electro-optic crystal, where a large number of relevant experimental data are available. The model explains the strong nonlinear dependence of the defect creation rates as a function of electronic stopping power (thresholding behavior). It also satisfactorily accounts for the formation and growth of amorphous layers by ion-beam irradiation at moderate fluences, f410 13 cm À2 . Moreover, it also provides the right trend and reasonable quantitative accordance to data showing the dependence of the track radius on stopping power in single-impact experiments. Finally, the model determines the light emission yield during irradiation. In particular, it predicts that the number of photons emitted by ion impact first increases and then decreases monotonically with increasing electronic stopping power. r
The appearance of light intensity thresholds for catastrophic optical damage in LiNbO3 is satisfactorily explained by using a photorefractive model based on the Fe(2+)?Fe(3+) and NbLi(4+)?NbLi(5+) defect pairs. Model simulations of the photorefractive amplification gain as a function of the light intensity present sharp threshold behavior. A similar behavior is shown by the saturating refractive index change. In agreement with experiments, predicted thresholds appear shifted towards higher intensities (up to a 10(4) factor) when the Nb(Li) concentration is decreased or the temperature is increased. The model also explains very recent data on the threshold enhancement with the Fe(2+)/Fe(3+) ratio in optical waveguides.
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