Although diamond photonics has driven considerable interest and usefulapplications, as shown in frequency generation devices and single photonemitters, fundamental studies on the third-order optical nonlinearities ofdiamond are still scarce, stalling the development of an integrated platformfor nonlinear and quantum optics. The purpose of this paper is to contribute tothose studies by measuring the spectra of two-photon absorption coefficient($\beta$) and the nonlinear index of refraction (n$_2$) of diamond usingfemtosecond laser pulses, in a wide spectral range. These measurements show themagnitude of $\beta$ increasing from 0.07 to 0.23 cm/GW, as it approaches thebandgap energy, in the region from 3.18 to 4.77 eV (390 - 260 nm), whereas then$_2$ varies from zero to 1.7E-19 m$^2$/W in the full measured range, from 0.83- 4.77 eV (1500 - 260 nm). The experimental results are compared withtheoretical models for nonlinear absorption and refraction in indirect gapsemiconductors, indicating the two-photon absorption as the dominant effect inthe dispersion of the third-order nonlinear susceptibility. These data,together with optical Kerr gate measurements, also provided here, are offoremost relevance to the understanding of ultrafast optical processes indiamond and its nonlinear properties.
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