Disclosed is a supercontinuum radiation source comprising a modulator being operable to modulate pump laser radiation comprising a train of radiation pulses to provide modulated pump laser radiation, said modulation being such to selectively provide a burst of said pulses; and a hollow-core photonic crystal fiber being operable to receive the modulated pump laser radiation and excite a working medium contained within the hollow-core photonic crystal fiber so as to generate supercontinuum radiation.