# Polarization and Malus's Law

1. Jan 1, 2014

### james walshe

Hi there all,
I am a little confused about polarization. If I have a laser beam incident on a single polariser, if I adjust the angle of the polarizers transmission axis so that it is aligned with the plane of polarization of the incident laser beam does it intensity remain unchanged, or does it lose 50% of its intensity due to Malus's Law?. Also can a polarizer change the polarisation state of the incident beam or will the transmitted beam always be linearly polarised?.

2. Jan 1, 2014

### Redbelly98

Staff Emeritus
Hi, welcome to PF.

If the laser beam is linearly polarized, and it's an ideal polarizer, then 100% of the beam is transmitted when the laser polarization is aligned with the polarizer -- in accordance with Malus's Law:

$$\frac{I}{I_{inc}}= \cos^2 \theta \text{, with } \theta=0$$

If the laser beam is circularly polarized or randomly polarized, then 50% is transmitted.

The transmitted beam will remain linearly polarized, but change in orientation, as the polarizer is rotated.

Hope that helps.

Last edited: Jan 1, 2014