Encyclopedia … combined with a great Buyer's Guide!

# Conflicting Definitions of S and P Polarization

Posted on 2012-03-03 as part of the Photonics Spotlight (available as e-mail newsletter!)

Abstract: There are conflicting definitions of s and p polarization in the scientific literature. What some people call p polarization, is s polarization for others. Obviously, that can cause confusion.

It is quite common to talk about s-polarized and p-polarized laser beams, incident on optical surfaces or diffraction gratings. Therefore, it is quite disturbing that there are conflicting definitions in the scientific literature:

• Usually, p-polarized light is understood to have an electric field direction parallel to the plane of incidence on a device, and s-polarized light has the electric field oriented perpendicular to that plane. (Actually, the letters have a German origin: s = senkrecht = perpendicular, p = parallel.) According to that definition, we can obtain vanishing reflectivity of a surface at Brewster's angle for p polarization. That's easy to remember: “p” is closer to “B” (like “Brewster”), so Brewster's trick works with p polarization.
• In the context of diffraction gratings, the opposite definition can be found. Here, “s” still means perpendicular, but in that case perpendicular not to the plane of incidence, but to the lines of the grating. So for s polarization, the electric field vector is perpendicular to the lines, i.e., it lies in the plane of incidence.

So there is another trap to fall into! When reading some paper, we have to find out which definition has been used.

By the way, some people call a laser beam s-polarized, when its polarization is vertical, i.e., perpendicular to the lab's floor. It is better, though, to restrict the terms s polarization and p polarization to cases where the polarization direction with respect to a plane of incidence is relevant. For example, if you have a Brewster-angled prism in the common orientation where the reflected beam stays horizontal in direction, s polarization according to the first definition above is vertical. However, if you turn the prism such that the reflected beam goes upwards, that will change, of course.

Note that you can also receive the articles in the form of a newsletter or with an RSS feed.

## Questions and Comments from Users

2020-07-30

Wikipedia says that TE = s, TM = p. Are these notations completely replaceable? I don't think so, but I couldn't find clear explanation of it.

Indeed I found such a statement on the page https://en.wikipedia.org/wiki/Polarization_(waves) (under “s and p designations”), and some others sources show similar things. However, I don't agree with that. In my opinion, one should not use the terms transverse-electric and transverse-magnetic (https://en.wikipedia.org/wiki/Transverse_mode) in the context of electromagnetic waves propagating in a simple homogeneous medium, where both electric and magnetic fields are perpendicular to the propagation direction. These terms are appropriate in the context of waveguide modes and the like, where we do have guided light. TE then means that the electric field is perpendicular to the propagation direction, while the magnetic field is not; a plane of incidence does not occur there.

2021-08-30

When there is normal incidence, how can I define the plane of incidence and s and p polarizations?

These are then no longer relevant: the optical effects will not depend on the polarization direction, assuming non-birefringent materials.

Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author’s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.

Spam check:

By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.

``<a href="https://www.rp-photonics.com/spotlight_2012_03_03.html">Article on Conflicting Definitions of s and p Polarization</a>in the <a href="https://www.rp-photonics.com/encyclopedia.html">RP Photonics Encyclopedia</a>``
``<a href="https://www.rp-photonics.com/spotlight_2012_03_03.html"><img src="https://www.rp-photonics.com/previews/spotlight_2012_03_03.png" alt="article" style="width:400px"></a>``