Is it possible to find refractive index from diffraction?

Homework Statement

I am trying to find the refractive index nylon (fishing line) , however when I used a laser onto the fishing line (nylon) it looked like it diffracted.

Homework Equations

I am able to find the diffraction if that was what it was showing, however I dont know how to calculate after that.

https://www.dropbox.com/s/k083dkj18xcdgro/CIMG3662.JPG?dl=0
https://www.dropbox.com/s/nq0d2iwd2kjem74/CIMG3664.JPG?dl=0
https://www.dropbox.com/s/ew0ys9dfqa1f4ol/CIMG3665.JPG?dl=0
https://www.dropbox.com/s/vs4nieam2yxy1t7/CIMG3666.JPG?dl=0

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