Study of the mechanical properties of thin films involved in ophthalmic glasses

Abstract

The mechanical properties of thin films involved in the manufacturing of ophthalmic glasses have been investigated by two complementary laser based techniques. On the one hand, picosecond ultrasonics (PU) measurements allows to determine the acoustical longitudinal velocity in the sample, hence the elastic constant c11. On the other hand, Brillouin light scattering (BLS) measurements leads to the value of the transverse velocity, hence c44. In the case of isotropic materials, these two coefficients give a direct access to the value of the Young’s modulus and Poisson’s ratio of the film. The influence of the film characteristics on its mechanical properties will be discussed, mainly regarding its thickness and the manufacturing process. Another issue concerning the effect of the film environment will be addressed. Especially, we will discuss the influence of the substrate on the mechanical properties of a single film, and the link between the mechanical properties of a single film and the ones of a films stacking.