| 摘要 |
A window, for receiving a modulated beam of light, restricts the field of view of an optical system by total internal reflection. The window rejects the entry of unwanted radiation, such as noise, and comprises first and second triangularly shaped wedges 16, 20 of optical material. An entry face 36 of the first wedge 16 is perpendicular to a base plane 21, and its rear face 38 is at an acute angle to the entry face 36. An entry face 40 of the second wedge 20 is at the same angle to the base plane 21 as the rear face 38 of the first wedge 16, and the two wedges 16, 20 are separated by an air gap. Preferably, the rear face 38 of the first wedge 16 is contoured to reject incoming radiation from below the base plane 21, with comparable contouring of the adjacent faces of the first and second wedges 16, 20 permitting the entry of skew rays, to increase the directions in which desired radiation is admitted to the optical system. |
