Vacuum ultra-violet (VUV) laser harmonics have been generated in a noble gas jet, which, combined with a standard spectrophotometer, have allowed measurements of the reflectance of porous silicon over a wide energy spectral range from 1 to 16 eV. Porous silicon dielectric function was, then, deduced from reflectance measurements by Kramers–Kronig analysis. Data are found to be in good agreement with those reported in literature, thus showing that laser harmonics represent a new, alternative, and suitable VUV source for optical characterisation of materials such as semiconductors and thin films.