a supercontinuum source for generating a supercontinuum;

a fibre bundle, wherein the fibre bundle includes a plurality of optical fibres for guiding the light; and

a depolarizing homogenizer, configured to receive light derived from the supercontinuum source, comprising:

one or more lenslet arrays, adapted for providing a plurality of beamlets associated with different respective parts of a received beam, wherein the one or more lenslet arrays comprise a first lenslet array and a second lenslet array, wherein the first and second lenslet arrays are oriented with respect to one another such that the lenslets of the first and second lenslet arrays are perpendicular to one another, wherein the lenslets of the first and second lenslet arrays are non-symmetric lenslets;

a depolarizer comprising different areas which affect polarization differently, wherein the depolarizer is positioned to cause alteration of the polarization characteristics of at least some of said plurality of beamlets; and

a lens arranged to at least partially overlap the said beamlets having said altered polarization characteristics, to provide an output beam,

wherein the one or more lenslet arrays comprise a plurality of lenslets shaped to cause the output beam to have a flat top beam profile in the image plane of the lens,

wherein the depolarizer is located between an output of the fibre bundle and an image plane of the lens,

wherein the fibre bundle is configured such that when light propagates through the fibre bundle, then the fibre bundle contributes to affecting the polarization.