A source control arrangement for a radiation source comprising a hollow-core photonic crystal fiber (HC-PCF) having a hollow core with a core diameter, comprising: at least one processor; and a pulse chirping arrangement configured to receive pulsed pump radiation and controllably chirp the pulsed pump radiation so as to output chirped pulsed pump radiation for exciting a working medium comprised within the hollow core of the fiber at a pressure. The at least one processor is operable to configure source parameters of the radiation source, which include one or both of the pressure and a pulse chirp parameter, such that the chirped pulsed pump radiation undergoes a spectral broadening process within the HC-PCF, thereby generating an output radiation having a predefined spectrum for a reference core diameter of the HC-PCF, so as to compensate for variation in the core diameter with respect to the reference core diameter.