Influence of object roughness on specimen gratings for moire interferometry

Moire interferometry is a high-sensitivity method for whole-field, in-plane displacement measuring. This technique requires the surface under test to be mirror-like and prepared with a fine diffraction grating (typically simi lar to 1200 lines/mm). Gratings are commonly made of photoresist. However, if we want to analyze engineering structures, to have a surface without pre paration under polishing, the surface roughness is an important parameter t o be characterized. We analyze the fringe visibility of moire during the fa brication of specimen gratings in function of the surface object roughness. The surface object target is impregnated with photoresist Shipley S1822. T wo beams from a He-Cd laser illuminating the surface target are used to rec ord the specimen grating. With a similar optical system we use a He-Ne lase r to obtain a virtual grating and consequently the interferometric moire fr inges. Through the correlation length and basic statistical the surface rou ghness is characterized. (C) 2001 Society of Photo-Optical Instrumentation Engineers.