A supercontinuum radiation source comprises: a radiation source, an optical amplifier and a non-linear optical medium. The radiation source is operable to produce a pulsed radiation beam. The optical amplifier is configured to receive the pulsed radiation beam and increase an intensity of the pulsed radiation beam. The non-linear optical medium is configured to receive the amplified pulsed radiation beam and to broaden its spectrum so as to generate a supercontinuum radiation beam. The optical amplifier may supply a pump radiation beam to a gain medium, an intensity of the pump radiation beam being periodic and having a pump frequency that is an integer multiple of the frequency of the pulsed radiation beam. The optical amplifier may supply pump energy to a gain medium only when the pulses of the pulsed radiation beam propagate through the gain medium.