DETERMINATION OF SMALL ANGULAR DISPLACEMENT BY MOIRE FRINGES OF MATCHED RADIAL-PARALLEL GRATINGS

We investigate the properties of the moire fringes of matched radial-p arallel (MRP) gratings that are useful for the fine visual indication of angular displacements. Moire patterns formed by overlapping two dif ferent MRP gratings of angular pitches, P-theta and P-theta' (<P-theta ) can provide a simple fringe-counting method for determining both the angle and the direction of the relative angular displacement of the g ratings within the accuracy of (P-theta'/M-theta), where M-theta is th e angular magnification for radial vernier fringes. (C) 1997 Optical S ociety of America.