# Finding Degree of Linear Polarization

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1. Dec 28, 2015

### pyroartist

I would like to measure the DoLP of outside daylight at the horizon with the sun overhead (midday in summer). Found this equation: DoLP = (reflectanceS - reflectanceP) / (reflectanceS + reflectanceP)
Where S and P are defined:
“The two orthogonal polarization planes are s, perpendicular to the plane of incidence defined by the
surface normal and the incident ray, and p, parallel to the plane of incidence.”
(A diagram showing what this statement refers to would be helpful as I am not familar with the terms used.)
I know that to get the S and P amplitude values I need to measure the light through a linear polarizer turned to one angle and then a different angle. Can someone tell me what two angles I need to rotate the polarizer?

Thanks!

2. Dec 28, 2015

### blue_leaf77

The English equivalent of S and P components are TE (transverse electric) and TM (transverse magnetic), respectively.
See pictures below for the orientation of each case:

Based on the above pictures, how do you conclude about the angle through which you will have to rotate your polarizer?

3. Dec 28, 2015

### pyroartist

It looks like they are 90 degrees apart, right?

4. Dec 28, 2015

### blue_leaf77

Right.

5. Dec 29, 2015

### pyroartist

Just one more question. How do you determine where to set a piece of linear polarizing film to get zero degrees?
Or can you just take any position and call that zero?
Thanks so much for your help!!

6. Dec 29, 2015

### Andy Resnick

The accurate method is to first get a rough idea of the angle by finding the minimum transmission, then rotating your polarizer 45 degrees and fine-tuning the angle such that you are at the halfway point: slight rotations CW and CCW will produce equal and opposite changes in transmitted intensity. Once that orientation is set, rotate precisely 45 degrees one way or the other.