The disclosure relates to a tunable optical light source spanning the UV-range and possible also the visible and near-IR wavelengths. The tunable optical light source includes an input light source, a focusing element, a non-linear crystal arranged to convert the frequency of at least part of the output spectrum of the super continuum source, and a holding unit for the non-linear crystal. The input light source is a super continuum light source with a spectral bandwidth of at least about 300 nm and the holding unit is adjustable for changing the frequency converted output wavelength of the non-linear crystal wfc such that the lowest obtainable output wavelength wUV of said tunable light source is ultraviolet. The disclosure further relates to an illumination source and an optical measurement system.