The use of third-harmonic generation of visible pulses in a magnesium-fluoride wedge has been proposed in order to obtain ultrashort pulses with photon energy in the vacuum ultraviolet range. Starting from a 200 fs blue pulse with 18 \ensuremath{\mu}J of energy (which is the second harmonic of the IR pulses produced by a regenerative Ti-Sapphire laser system), ${10}^{3}$ photons were obtained at 9.4 eV, with ${10}^{\ensuremath{-}9}$ conversion efficiency. From the measurements it was inferred that ${\ensuremath{\chi}}^{(3)}(\ensuremath{-}3\ensuremath{\omega};\ensuremath{\omega},\ensuremath{\omega},\ensuremath{\omega})\ensuremath{\approx}0.45\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}{\mathrm{m}}^{2}/{\mathrm{V}}^{2}$ for the third-order susceptibility of magnesium fluoride. The simplicity of the arrangement makes this approach ideal for the generation of the ultraviolet probe required by time and angle-resolved photoemission spectroscopy.