Techniques: A Multiplexed Grating Shearing Interferometer for Reflection Moiré Analysis of Partial Slopes and Curvatures of Bent Plates

Simultaneous and real-time measurement of slope and curvature fringes in thin structures using shearing interferometery

“…This observation has been widely utilized by a number of investigators in the past to measure surface slopes and curvatures separately using both coherent and incoherent optical metrology. These methods can be broadly classified into 1. real-time methods [2][3][4][5][6] and double-exposure schemes 7,8 involving specularly reflective objects, and 2. double-exposure schemes for diffusely reflective surfaces. 9,10 Among the real-time slope and curvature measurement methods for specular objects, Assa, Betser, and Politch 3 have demonstrated different grating shearing interferometers.…”

“…A modified reflection moiré method proposed by Ritter and Schettler-Koehler 4 is capable of providing curvature fringes in real time. Selective diffraction order filtering is utilized by Subramanian et al 5,6 to obtain slopes and curvatures sequentially in real time. Subsequent optical spatial filtering is needed in some arrangements to acquire the necessary information.…”