Optical properties of a laminated sheet are investigated as a two-ply
film. Retardations of the laminated sheet could not be obtained withou
t separating it into individual films. A new method presented here mak
es it possible to determine three optical constants of two-ply phase p
lates: two optical pass differences and their relative azimuth angle.
Experimental values of known samples which are in agreements with calc
ulated values are obtained by the new method.