MULTI-PASS OPTICAL APPARATUS

An apparatus includes a first plurality of concave reflecting surfaces; a second plurality of reflecting surfaces facing the first plurality of concave reflecting surfaces such that a region is defined between the first and second pluralities; and an input for an optical beam to enter the region and an output for the optical beam to exit the region. The first and second pluralities of reflecting surfaces are arranged relative to each other so that the optical beam is re-imaged at a reflecting surface of one of the pluralities after only one reflection from a reflecting surface of the other of the pluralities and so that overlap of two or more optical beams on each of the reflecting surfaces is avoided.