An apparatus includes a base that includes a raised surface and a first opening through the raised surface. The apparatus also includes a cover configured to be coupled to the base in order to form a cavity, where the cover includes a second opening through the cover. The raised surface is configured to allow passage of a first portion of optical energy through the first opening and to reflect a second portion of the optical energy. Portions of the cover and the base surrounding the cavity are configured to absorb the reflected second portion of the optical energy. The base may further include one or more baffles positioned around the raised surface, and/or the cover may further include one or more baffles positioned around the second opening.