Variable repetition rate and wavelength optical pulse source, comprising a fixed or variable repetition rate source of supercontinuum pulses; a wavelength tunable optical bandpass filter to filter the supercontinuum pulses at two or more wavelengths, wherein said source of supercontinuum pulses and said wavelength tunable optical bandpass filter are configured such that the optical pulse source can provide variable repetition rate and variable wavelength optical pulses including a series of repetition rates with selected wavelength-varying pulse trains.