Holographic Scanning UV Telescope for the Tropospheric Wind Lidar Technology Experiment

The first ever ultraviolet (UV) telescope based on a transmission Holographic Optical Element (HOE) as the primary optic has recently been completed as part of the Tropospheric Wind Lidar Technology Experiment (TWiLiTE). This article describes the TWiLiTE instrument, its function, and status. The HOE is mounted in a ring bearing and rotates about its center normal to generate a 45° conical scan while the remainder of the telescope remains stationary. Preceded by two similar telescopes at visible and near IR wavelengths, this is the first UV version of a HOE based telescope. The TWiLiTE instrument is designed for use in the uncontrolled environment of the instrument bay in the high altitude NASA WB-57 aircraft. The TWiLiTE will use the HOE telescope with a pulsed UV laser to profile tropospheric winds from the aircraft's cruise altitude of ∼18 km down to the surface. The HOE is 40 cm in diameter, 1 cm thick, has a 1 m focal length and a 45° off-normal field of view. The telescope is a twice-folded coaxial design, with a flat secondary and a convex tertiary mirror that directs the light through a hole in the secondary. A 2 cm diameter laser beam is transmitted coaxially through a two mirror periscope mounted in a hole in the center of the HOE.