A method for optically pumping a gain-medium with partially polarized or unpolarized pump-light having a wavelength at which that gain-medium has an absorption that is dependent on the polarization plane of the pump-light is disclosed. The pump-light is directed into the gain-medium. The strongest-absorbed polarization component of the pump-light is substantially absorbed and the weakest-absorbed polarization component is partially transmitted by the gain-medium. The polarization plane of the transmitted component is rotated through 90 degrees and the polarization-rotated pump-light is directed back into the gain-medium, wherein it is substantially absorbed.