Multiple-beam Fizeau fringes are used to study the changes in optical
properties of Nylon-6 gamma-irradiated fibres. Changes in fibre struct
ures due to dl awing have been studied using two-beam interference. So
me structural parameters such as optical orientation function and elec
tric polarizability difference (Delta alpha/3 alpha(O)) were determine
d. Delta alpha/3 alpha(O) is found to be constant and depends only on
the fibre structure. The generalized Lorantz-Loranz equation given by
de Vries is used to determine Nylon-6 fibre structural parameters. Com
parison between the results and when using Lorantz-Loranz equation are
given. Refractive index profiles also can help in fibre investigation
s.