Room-temperature upconversion emission up to eight-photon absorption is demonstrated from diamond single crystals under femtosecond laser excitation for the first time. The low concentration of defects and impurities is attributed to the support of free excitons emission at 235 nm. Nonlinear optical properties are also investigated by using an open-aperture Z-scan technique. The corresponding three-, five-, and eight-photon absorption coefficients of the diamonds are found to be 1.8 × 10-2 cm3/GW2, 5 × 10-9 cm7/GW4, and 1.6 × 10-19 cm13/GW7, respectively. Considering its high hardness and high thermal conductivity, diamonds are a versatile nonlinear optical material suitable for high-power deep ultraviolet applications under multiphoton excitation.
Keywords: diamond single crystals; nonlinear optical absorption; nonlinear optics; photoluminescence; upconversion emission.