A method of combining and co-aligning a plurality of radiation beams each having a respective waveband, includes the steps of passing each of said radiation beams to a respective lateral deflector to impart a selected lateral displacement to said beam. Each of said radiation beams with respective imparted lateral displacements is then passed to an optical collimating element which passes said radiation beams to an optical deflecting element which applies a wavelength dependent deflection to the radiation beams. The respective lateral displacements are selected having regard to the waveband of each beam to cause all to exit the optical deflecting element at the same angle so they are co-aligned.