MEASURING THE THICKNESS AND REFRACTIVE-INDEX OF A THICK TRANSPARENT PLATE BY AN UNEXPANDED LASER-BEAM

The thickness and refractive index of a thick transparent plate are me asured by using an unexpanded HeNe laser beam. The laser beam is incid ent at different angles onto the plate, and then two reflected beams, from the front and back surfaces, are received on a distant screen: th e corresponding separations between them are measured. A theoretical r elation between the refractive index, thickness, angle of incidence an d separation is derived. This relation is experimentally verified and shows good agreement. The errors in the measured thickness and refract ive index are analysed. The method is non-contact, non-destructive and low cost. (C) 1997 Elsevier Science Ltd.