Diffractive optics for moon topography mapping

This paper presents the design, analysis, and testing of a diffractive optical element (DOE) to be part of the Lunar Orbiter Laser Altimeter (LOLA) instrument scheduled to launch in 2008. LOLA will be one of six instruments to orbit the Moon for a year or more as part of the Lunar Reconnaissance Orbiter (LRO). The various scientific instruments aboard the LRO will map the lunar environment in greater detail than ever before. LOLA will produce a topographic map of the Moon from a nominal 50km orbit during the one-year mission. LOLA works by bouncing laser pulses off the lunar surface as it orbits the Moon. By measuring the time it takes for light to travel to the surface and back, LOLA can calculate the roundtrip distance. Each pulse consists of five laser spots in a cross-like pattern spanning about 50 meters of the lunar surface. The spots are generated by a DOE from the single, collimated LOLA laser input beam. It is projected that LOLA will gather more than a billion measurements of the Moon's surface elevation creating a high resolution three-dimensional map of the surface.