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.