A laser radiation source for a lithographic tool comprising a laser module to emit a first laser beam having a first wavelength and a second laser beam having a second wavelength, a beam separation device to separate the optical paths of the first and second laser beams and substantially recombine the optical paths, a beam delivery system to direct the first and second laser beams to a fuel target and an optical isolation apparatus to: adjust the polarization state of the first laser beam, adjust the polarization state of the second laser beam and to block radiation having the adjusted polarization states such that the reflection of the first laser beam and the reflection of the second laser beam are substantially blocked from propagating towards the laser module.