Two-photon absorption and nonlinear refraction in commercial colour glass filters

We report the measurement of two-photon absorption coefficients , free-carrier absorption cross sections and nonlinear refraction coefficients in the transparency region of a large number of commercial colour glass filters of different manufacturers. The measurements were performed by z-scan and by monitoring the energy transmission of a 6 ps Nd:glass laser pulse at a wavelength of 1.054 m. The nonlinear refraction is primarily due to the two-photon-generated free carriers and has a negative sign. For Schott filters the magnitudes of nonlinear refraction per electron-hole pair are in agreement with those reported in the literature. The magnitude of changes by an order of magnitude for different filters, however, at a given ratio of photon energy/bandgap, the change in is less than a factor of two in filters of different manufacturers.

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