A mounted hollow-core fiber arrangement includes a hollow-core fiber having a microstructure, and a mount arrangement including a plurality of mounting contacts configured to apply a force to an outer layer of the hollow-core fiber. A portion of the hollow-core fiber is located in a receiving region of the mount arrangement. The plurality of mounting contacts are positioned around the receiving region. The mounting contacts are distributed around the receiving region, the distribution of the mounting contacts corresponding to a distribution of features of the microstructure of the hollow-core fiber. The mounted hollow core fiber can be used in a radiation source apparatus for providing broadband radiation.