Enhancement of optical nonlinearity of heavy-metal oxide glasses by replacing lead and bismuth with thallium

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Abstract
We report on the results of degenerate four‐wave mixing experiments at a wavelength of 1.06 μm on a number of heavy‐metal gallate glasses. The replacement of lead (Pb) and/or bismuth (Bi) by thallium (Tl) leads to an enhancement of the optical nonlinearity, resulting in the largest nonresonant electronic nonlinearity yet reported for an oxide glass. χ(3) is proportional to the concentration of Tl; samples with more than 25 cation % Tl have χ(3) larger than that of carbon disulfide (CS2). The optical nonlinearity has an off‐resonant electronic origin, which is confirmed by measurements of the diagonal and off‐diagonal components of the χ(3) tensor.