Influence of object roughness on specimen gratings for moire´ interferometry

Abstract

Moireinterferometry is a high-sensitivity method for whole- field, in-plane displacement measuring. This technique requires the sur- face under test to be mirror-like and prepared with a fine diffraction grat- ing (typically ;1200 lines/mm). Gratings are commonly made of photoresist. However, if we want to analyze engineering structures, to have a surface without preparation under polishing, the surface rough- ness is an important parameter to be characterized. We analyze the fringe visibility of moireduring the fabrication of specimen gratings in function of the surface object roughness. The surface object target is impregnated with photoresist Shipley S1822. Two beams from a He-Cd laser illuminating the surface target are used to record the specimen grating. With a similar optical system we use a He-Ne laser to obtain a virtual grating and consequently the interferometric moirefringes. Through the correlation length and basic statistical the surface rough- ness is characterized. © 2001 Society of Photo-Optical Instrumentation Engineers.