Abstract: The invention disclosed herein relates to fibre lasers with intra-cavity frequency doubling. In one embodiment, the invention is directed to a fibre laser with intra-cavity frequency doubling characterized in that a non-linear crystal of type II phase matching is used to thereby enable operation of the fibre laser without selection of polarisation of the generated fundamental radiation. The non-linear crystal is oriented so as to minimise the walk-off angle of the second harmonic radiation, and a second dichroic mirror together with one of a plurality of focusing elements forms a telescopic reflector that provides for focusing and compensation of the spatial walk-off effect of the non-linear crystal.