An optical parametric generator comprises a seed laser feeding an optical system. The seed laser is arranged to provide a seed beam at either a signal frequency of a signal wave or an idler frequency of an idler wave. Further, the optical parametric generator comprises a pump laser of a defined type feeding the optical system. The pump laser emits ultra-short optical pulses as a pump wave. In addition, the optical parametric generator comprises a second order non-linear crystal of a defined type arranged in the optical system. The defined type of the crystal and the defined type of the pump laser are selected so that the signal wave or the idler wave are locked in an edge of the pump wave.