First-Principles Calculations of the Urbach Tail in the Optical Absorption Spectra of Silica Glass

Abstract

We present density-functional theory calculations of the optical absorption spectra of silica glass for temperatures up to 2400 K. The calculated spectra exhibit exponential tails near the fundamental absorption edge that follow the Urbach rule in good agreement with experiments. We discuss the accuracy of our results by comparing to hybrid exchange correlation functionals. We show that the Urbach rule holds in a frequency interval where optical absorption is Poisson distributed with very large statistical fluctuations. In this regime, a direct relation between the optical absorption coefficient and electronic density of states is derived, which provides a link between photoemission and absorption spectra and is used to determine the lower bound to the Urbach frequency regime.

Strong nonlinear growth of energy coupling during laser irradiation of transparent dielectrics and its significance for laser induced damage

“…Based on this approach, it is shown how damage initiation may occur because of a strong nonlinear growth of energy coupling. In particular, the formation of an absorption front (AF), moving at a speed one order of magnitude slower than the sound speed, is predicted, consistent with experiments [24] and other models [21]. This mechanism is essentially expected at the beginning of the interaction where the material undergoes major change of its electronic, optical and structural properties.…”

“…More recently, observation of induced absorption in glasses due to ultrashort laser pulse exposure has also been reported [20]. Additionally, recent density-functional theory calculations [21] have shown that silica absorption spectra are expected to exhibit exponential tails near the band edge at elevated tempertatures.…”

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Electronic structure of LaBr3from quasiparticle self-consistentGWcalculations

“…On a single-particle level, the latter is related to the dielectric function and thus the absorption coefficient as discussed for example, in Ref. 59. One can therefore expect a correlation between characteristic features in the absorption spectrum with features in the JDOS.…”