A stepped etalon having a top surface and two bottom surfaces that are
parallel to the top surface and are each positioned at different
distances from the top surface. Each bottom surface has an edge, wherein
the edges face one another and a sloping step is positioned between the
two edges so that rays from a beam of light projected onto the top
surface of the etalon strike the step at the Brewster angle and pass
through the etalon without any light being reflected back therein.