Polarimetric studies of polyethylene terephtalate flexible substrates

¹ Horiba Jobin Yvon SAS, 5 avenue Arago, 91380 Chilly-Mazarin, France
² LPICM, École Polytechnique, CNRS, 91128 Palaiseau, France
³ UCCS-Artois, UMR CNRS 8181, Université d'Artois, 62307 Lens, France

Corresponding authors: michel.stchakovsky@jobinyvon.fr enric.garcia-caurel@polytechnique.edu

Received: 31 January 2008
Revised: 13 June 2008
Accepted: 25 July 2008
Published online: 6 December 2008

Abstract

Polymer sheets are currently used worldwide in a wide range of applications. The manufacturing process of these sheets involves extruding machines that stretch the material in both lateral and longitudinal directions with respect to the machine direction, thus inducing birefringence. In most cases, the film obtained is optically biaxial. Polarimetric spectroscopy (Ellipsometry and Mueller Matrix) combined with conoscopic observation are the methods of choice to study these properties. In this work we report an analysis of commercially available polyethylene terephtalate (PET) films used as substrate for food packaging as well as for embedded electronic devices such as solar cells or flexible displays. Initial observation of these films through polarizing microscope in conoscopic mode reveals first the trace of optical axis plane with respect to the film surface and second, whether the optical axis is acute or not. This preliminary study allows optimal sample positioning for further polarimetric studies. The measurements and modelling are done in both reflection and transmission mode on several spectroscopic polarimetric setups from UV to NIR. The models give as a main result, the dielectric tensor of the film as well as its orientation with respect to the laboratory reference frame.