Optical pulse source, for generating optical supercontinuum pulses, comprising: an optical pump laser operable to generate a number of optical pump pulses at a pump pulse repetition rate; a nonlinear optical element arranged to receive optical pump pulses and configured to generate therefrom optical supercontinuum pulses; and a gating device provided between the pump laser and the nonlinear optical element and operable to selectively limit the number of optical pump pulses received by the nonlinear optical element in order to generate optical supercontinuum pulses at a user selectable repetition rate lower than the pump pulse repetition rate, wherein the optical pulse source further comprises a second gating device provided after the nonlinear optical element.