The Star Generator: A novel device for optical characterization of large-area primary objective gratings

Our research in the field of Primary Objective Grating (POG) telescopy requires the manufacture and characterization of large area diffraction gratings, and thus the ability to test and characterize their optical properties. Here we report on a novel device for the generation of highly spatially coherent arbitrary light fields, termed the 'Star Generator'. The Star Generator consists of a Texas Instruments DLP4710 micromirror array placed at the focal point of a 30in parabolic reflector. The DLP array contains over 2,000,000 micron scale tip-tilt electromechanical mirrors, and allows for two-state tilt control of each individual micromirror in the array. Our application utilizes the mirrors of the DLP array to act as pinholes in the focal plane of a large collimating mirror. The relative size of each 5 mu m DLP mirror compared to the 30in diameter reflector results in collimated light of coherence length on the order of the reflector, thus creating a fully programmable field of over 2,000,000 point-like sources, with the ability to simulate a dense star field of arbitrary configuration. The achromatic nature of DLP allows for almost any light source to serve in generating the star field, with High Intensity Discharge lamps or diffused lasers being good candidates for replication of stellar spectra and single wavelength (narrow band) experiments. The Star Generator will allow our collaboration to test and characterize the optical properties of dispersive primary objectives, with the benefit that these tests can take place in a highly controlled environment and serve a wide array of functions.