Re: polarizing microscope for the refractive index calculation

Perhaps some terminology can help here.  Materials are isotropic, uniaxial or 
biaxial.  In the first of these, there is only one refractive index for the 
material, no matter which way you look at it.  In the second case, there are 
two refractive indices, one in a certain direction (the axis) and a second in 
any direction perpendicular to the first.  Biaxial materials have three 
refractive indices, Nx, Ny & Nz.  

At 3M we make and measure uniaxial and biaxial polymer films, so I'm sure 
someone in the company knows how to measure them, but I'd have to find them 
and see what they're allowed to say about the subject.  Here's a link to 
an instrument that can do the measurements you need:  
http://www.lambdaphoto.co.uk/products.php?r=150
-- 
Best regards,
Steve Eckhardt
skeckhardt at mmm dot com