A source module suitable for an optical coherence tomography system. The source module comprises a source 1 operable to emit a divergent, source output beam either of circular cross-section (e.g. as output by a vertical cavity surface emitting laser) or of elliptical cross-section (e.g. as output by an edge-emitting semiconductor laser or diode). Collimation optics 3 are provided to convert the source output beam into a non-divergent, collimated beam 4 of elliptical cross-section having a major axis and a minor axis. A cylindrical lens 6 is arranged with its piano axis aligned with the major axis of the elliptical collimated beam and its power axis aligned with the minor axis of the elliptical collimated beam so as to form a line focus extending along the major axis of the elliptical collimated beam.
