Estar, Melinex, Mylar的折射率
Poly(ethyleneterephthalate) also known as PET, Mylar, Melinex and Estar is a commodity polyester widely used in a variety of applications: films, bottles or as spun fibers. It is typically quite birefringent in sheet form with distinct refractive indices in all 3 dimensions. As a rule of thumb the in-plane indices increase as the film (or foil) thickness decreases. (At the same time the out-of-plane index decreases.) This is due to the biaxial stretching process used to attain both a desired film thickness and specific sheet mechanical properties. Even formally describing PET film as having a x, y, and z refractive index is not truly sufficient as there is a slight index grading in the thickness direction*. Suffice it to say while this is a very common, everyday material, it is also a surprisingly complicated optical system.
*Elman J.F., Greener J., Herzinger C.M., and Johs B. "Characterization of Biaxially-Stretched Plastic Films by Generalized Ellipsometry" Thin Solid Films 1998, 313/314, 814-818.
折射率引用 - Filmetrics composite