# polarizing axis of the polarizer

As I know, a linear polarizer is a transparent optical instrument (like a piece of glass) that has a polarizing axis. Electric field components of electromagnetic waves that are parallel to polarizing axis of the polarizer pass through it and those electric field components that are perpendicular to polarizing axis are absorbed by the polarizer. Hence, the polarizing axis is fixed in a polarizer and when we rotate it, the polarizing axis is also be rotated and if the incoming light was polarized, we see that the surface of polarizer gradually becomes dark and then light as we rotate it.

My question here is that, is there any polarizer that for changing it's polarizing axis, we don't have to rotate the polarizer itself, it means that the polarizer be placed fixed somewhere and we can change it's polarizing axis by using for example a handle. If it hasn't made any polarizer like this I described, basically is it possible to make such a polarizer or not?

• Well, it kinda depends. Do you count this sort of object as "rotating the polarizer itself"? The housing stays fixed, and it has a ring which physically rotates the polarizer glass. On the other extreme, even if you have, say, an LCD screen that changes its polarization properties when an external field is applied, you still have molecules physically rotating inside the crystal. So where do you draw the line? – Emilio Pisanty Nov 9 '16 at 16:39

As you said, a polarizer has a fixed axis. In a way you always have to rotate it so to change the polarizing direction.

However there are devices/materials which allow to externally control the axis without manual rotation.

This is mainly achieved by:

a)electronically controlled actuators, which rotate the filter as if you were rotating but in an automated way

b)more interestingly, there are materials who change their properties according to an external (i.e. electric) field.

A classical example are nematic crystals. Imagine a material made of aligned rods which, being anystropic, "let" the light pass only in a given direction. They can be rotated by an external field so to change the polarizing axis. That's how LCD works (:

• for example can we use polarizers in cars glasses so every time the people want they could change the polarizing axis of the polarizer in the glass by a button or by a handle to make the glass more darker or more lighter depending on the intensity of the sun light? – Masoud Nov 9 '16 at 15:51
• It is feasible theoretically only maybe of complex realisation. Plus solar light is unpolarised. Reflexes are polarised but I am not sure it would be that useful. Still it is feasible! – JalfredP Nov 9 '16 at 17:16