Off-axis reflective transmit telescope for a directed infrared countermeasures (dircm) system

Abstract

An off-axis reflective transmit telescope for a DIRCM system is mounted on the gimbal along a transmit-axis offset laterally from the optical axis of the receive telescope but nominally aligned with the line-of-sight of the receive telescope to transmit a laser beam. The telescope comprises an optical port optically coupled to a laser to receive and direct the laser beam away from the dome and a reflective optical assembly that reflects the laser beam through the dome. The reflective optical assembly comprises an off-axis mirror segment and a second optical element that together precompensate the laser beam for dome aberrations induced by the lateral offset of the transmit telescope's transmit axis from the optical axis. The off-axis mirror segment comprises a segment of a parent mirror having an aspheric curvature (e.g. parabolic, elliptical or higher-order asphere) about an axis of symmetry. The segment is offset so that it is not centered on the axis of symmetry of the parent mirror. The use of the off-axis mirror segment allows the optical port and any folding mirror to be positioned so that they do not obscure the reflected laser beam. The second optical element may be a segment of a dome corrector parent lens, a prism or a refractive lens formed on the front surface of the off-axis minor segment.