Apparatus for producing an interference pattern from an input optical beam, including a first optical element for separating the input optical beam into a plurality of divergent optical sub-beams and a second optical element including a first surface and a second surface. The first surface is optically coupled to the first optical element to receive at least two of the plurality of sub-beams. In addition, the second optical element is capable of redirecting via total internal reflection at least one of the sub-beams received at the first surface such that at least two sub-beams emerge from the second surface along respective paths intersecting one another outside the second optical element at a distance from the second surface. Advantageously, the use of total internal reflection in the second optical element for sub-beam redirection removes any requirement for a mirror to perform this function, results in only minimal power losses as the sub-beams reflect internally and the location at which they intersect is easily adjustable.