I have a throlabs half- and quarter-wave plate with rotation plate. There shown the angle scales and a line denotes the fast axis. But what does the angle mean? I do some research and someone said the angle reading tells the angle away from the transmission direction and other said that's the angle away from the fast axis. So here is the transmission direction same as the fast axis?
If I know the incoming light is linear polarized but don't know the orientation.
Is that possible to tell the orientation by using the half-wave plate?
Also, I am studying the same optics element. When I read the material of the polarized beam splitter, I know that the incident beam will be split by the splitter with the two perpendicular outgoing beams.
What really confusing is if the incident light is linear polarized, what can I tell about the outgoing beams after a splitter?
Can I say they are bother linear polarized and what about the polarized orientation?
The last question is pretty odd to me. In the text, it said we can use a quarter-wave plate to elliptical polarize a linear-polarized light. In some special case, the outgoing light could be circularly polarized. But how can I verify that? I tried the following: I let the linear-polarized light go through a half-wave plate so to control the orientation of the polarization, then let that light pass a quarter-wave plate. If I measure the power out of the quarter-wave plate, it is pretty constant. I think it doesn't tell if the beam is elliptical or circular because the power I measure is the average one, right? So I put a polarized beam splitter after the quarter-wave plate to observe the power of the split light. I think if the light is elliptical, the power should change with time, but again it is pretty constant. Doesn't matter how I rotate the quarter-wave or half-wave plate, the power is pretty constant.
Is that anything wrong with this testing way?
Best Answer
Have a look at this Wikipedia page, it explains the difference between a fast axis and a slow axis. But essentially it is to do with the properties of a birefringent crystal.
Firstly, you could consult the Thor Labs manual/booklet that you have got with the equipment, that should sort out your confusion for you. I'm guessing it is the angle away from the fast axis. But since (as far as I remember) the angular scale can be detached and put back onto the polarizer, it will help if you calibrate your polarizer with some known light before you make any measurements with it.
As daaxix has pointed out, you could use Stoke's parameters to characterize the light. There are several standard experiments in the literature to determine the Stoke's parameters.
If you send a linearly polarized beam through a quarter wave plate, it will in general come out elliptically polarized. You could confirm this by putting another polarizer (with a known polarization axis) after your first polarizer and rotate that with respect to the first polarizer, and then measure the intensity. The resulting intensity will be constant with angle if your light is circularly polarized, or it will vary (the variation will be larger than your experimental error) if the light is elliptically polarized.