Understanding the Principle of Birefringence: Δn Explained

[rwooduk]

I finally understand the principle of being able to imagine light as having 2 perpendicular components of electric field, to use an analogy from an earlier thread, its just as a weight on a slope may be considered to have 2 componants.

Anyway, for this example n_x = n_y = n_o and n_z = n_e. Light is traveling in the y direction therefore the perpendicular E components will be subject to n_x and n_e i.e. there will be birefringence.

My question is the question asks for Δn and I am unsure what this means. Do I just find a term for n_x - n_e?

Please see attached images to visualise the problem, 1 shows the problem, 2 shows the working for a similar problem, thanks in advance.

p.s. this is not part of any assessed homework

 

[rwooduk]

bump?