Modular Adaptive Optics Testbed for the Npoi

The Naval Prototype Optical Interferometer (NPOI) is a long-baseline, multi-station interferometer whose collection apertures can be relocated to provide flexible baseline lengths. While NPOI has the longest baseline at optical wavelengths in the world, the sensitivity of the interferometer is limited by the size of the individual collection apertures which are currently 0.5 meters in diameter. NPOI is currently upgrading its collection apertures to 1.4 meter diameter light weight telescopes to increase the sensitivity. At its location on the Anderson Mesa in Arizona, the chosen diameter of the telescope apertures is much larger than the average r0 of the site. As a result, adaptive optics must be used to correct for the wavefront aberrations. Several adaptive optics system configurations are suitable to provide the required wavefront correction, but it is highly desirable to have the adaptive optics systems as a component of the telescopes. This is being accomplished by designing the telescopes so that the adaptive optics system resides in the base of each telescope allowing a truly reconfigurable array. Thus evaluating and characterizing the performance of the adaptive optics systems is a critical component of identifying the desired adaptive optics system to support the move to larger aperture telescopes. This paper outlines a modular, electro-optical testbed that has been constructed for characterizing candidate adaptive optics systems for use at NPOI. The testbed makes use of innovative technologies to characterize the spatial and temporal performance of an adaptive optics system. Spatial performance is evaluated using a spatial light modulator liquid crystal device while temporal response is evaluated with a fast steering mirror that is used in series with the liquid crystal device. We report on the capabilities of the testbed and on the initial characterization of a low cost portable adaptive optics system.