Simulation of an optical model sensor for the pinhole/occulter facility

An optical modal control sensor (MCS) for use in vibration control of the pinhole/occulter facility (P/OF) has been designed and simulated. The MCS system comprises a He-Ne laser source, linear zone plates, linear photodiode arrays, and sample/hold and A/D converting circuits. The flexible modes of P/OF are detected by the deflection of the image focused by the zone plates. Three algorithms for laser beam centroid estimation are investigated: linear three point centroid, quadratic three point centroid, and probability density centroid. A comparison of estimating errors as functions of centroid location and beam size for the three different methods is made. These simulations account for the nonuniform response of the photodiode pixels