Optical configuration and optical tests of the HartRAO Lunar Laser Ranger

The telescope to be used for the HartRAO Lunar Laser Ranging system is a 1-m Classical Cassegrain donated by a French observatory called the Observatoire de la Cote d’Azur. Limited technical details of the telescope exist so tests were conducted to determine its optical characteristics and performance. The optical performance of the telescope was determined through its transmission efficiency. The optical efficiency of any telescope highly hinges on the reflectivity and surface accuracy of optics through which the laser signal is delivered. We present possible coude paths and their respective components for beaming the laser signal from its source and through the telescope. Spectroscopic measurements of each of the coude optics were conducted in order to determine the total throughput of the system. The surface accuracy of the primary mirror was validated by performing a structural analysis of the mirror under its support system. Taking into account the honeycomb geometry of the mirror, its material properties and support mechanism, a finite element analysis was done with ANSYS to predict the gravitational deformations the mirror will experience under operational angles. High optical performance telescopes require that deformations be kept to a small fraction of the wavelength of light the telescope is designed to use. A system efficiency of ~ 90% can be expected if obstructions and number of reflective surfaces are limited on the coude path.