How many oscillating fields exist in a light wave?

Question

Is light made from one magnetic and one electric field which are oscillating perpendicular to each other? In textbooks, it says that the light can be seen to oscillate in every plane perpendicular to direction of travel of the wave. This would imply that light has many oscillating electric and magnetic fields in a singular wave? What does it therefore mean by polarisation?

Answer 1

Disclaimer: It looks like we're talking in terms of classical electromagnetism, so that's what I'm going to do here. If you go all quantum mechanical or relativistic, the answers will be consistent, but different.

The simplest EM wave will have one oscillating E field and one oscillating B (magnetic) field. That wave will be polarized (i.e. E field is wiggling in one specific direction) and monochromatic (i.e. perfect sine wave).

Technically you could argue that the "simplest wave" is circularly polarized instead of linearly polarized, but for the purposes of your question, it doesn't matter. I'm just covering my pedantic backside by saying that.

Anything more complicated than your monochromatic, linearly polarized sine wave can usually be thought of as a COMBINATION of simple EM waves. For example, if you want a perfectly polarized light source that's more than a single frequency, you just take a bunch of simple polarized monochromatic waves of different frequency and add them together.

Here's an example of what I'm talking about plotted in desmos. This is a bunch of waves. Each is polarized in the same direction (i.e. up and down). Each has a different frequency.

Here's what the actual wave would look like (because the total E field at any given location comes from the SUM of all your separate individual E fields)

New example, if you want monochromatic but unpolarized light, then get a bunch of simple EM waves (i.e. sine waves where the E field is oscillating in a particular direction), each polarized in a different direction, and add them together. The only constraint is that for each simple single-wave building block, the B field has to be perpendicular to the E field. And both the E and B field have to be perpendicular to the direction your simple sine wave is traveling.

Here's an example of a lot of simple EM waves of different polarizations being added together. (Made in python)

These are all the simple sine waves considered separately.

And this would be the scalar E field you'd get when they're all added together.

So...

Is light made from one magnetic and one electric field?

Yes. Light is made from one B field and one E field. Technically, that's all you ever get, since the E and B fields that we actually see are the TOTAL E and B fields, where everything gets summed together at every point.

Is light made from one magnetic and one electric field which are oscillating perpendicular to each other?

It depends. E and B fields of individual simple EM waves must be perpendicular to each other. But if you have multiple individual simple EM waves of different polarizations all in the same place, then your TOTAL E and B fields must be a sum of all of them.

In textbooks, it says that the light can be seen to oscillate in every plane perpendicular to direction of travel of the wave.

That's correct. This is really just a different way of saying that the direction of oscillation of the E field must be perpendicular to the B field, and the two must be perpendicular to the direction the simple EM wave travels. So the plane perpendicular to the direction of travel contains all the different polarizations your simple EM wave COULD have.

This would imply that light has many oscillating electric and magnetic fields in a singular wave?

Hopefully this question has answered itself at this point. If you have a simple EM wave, then it only has one polarization (i.e. direction the E field wiggles). Real light is normally multiple simple EM waves all added together. I wouldn't think of that as multiple E and B fields in a singular wave. I'd think of it as multiple WAVES added together in a singular E and B field. I hope the distinction makes sense, because I think it's important.

What does it therefore mean by polarisation?

Polarization means "the direction the E field wiggles". If you have a bunch of simple EM waves all wiggling in the same direction, your resulting light will be polarized. If MOST of the simple EM waves are pointing in one direction but SOME are pointing in a different direction, then your light is MOSTLY polarized. If your simple EM waves are pretty much pointing in any direction allowed (where "allowed directions" are ones that lie on the plane perpendicular to the direction the light is traveling), then the light is unpolarized.

Answer 2

No one can measure directly that light from a thermal source or from a laser has wave properties. Only the intensity distribution behind an edge allows such conclusions.

Everyone should also be able to confirm that the only source of EM radiation is the emission of photons from excited subatomic particles. These photons are energy packets that have a magnetic field component and an electric field component. In thermal sources, these fields are randomly rotated in space (but both oriented 90° to each other and both 90° to the direction of propagation).

How many oscillating fields exist in a light wave?

1. from thermal sources comes a stream of unpolarised photons of the most varied frequencies (similar to blackbody radiation). There is no question of ONE wave. There is a wide frequency band of photons without any macroscopic wave properties.
2. from a laser comes a stream of unpolarised (if not filtered at the output) photons with a more or less narrow frequency band of photons. There are pulsed lasers, but lasers have nothing to do with a wave. Radio waves are generated by synchronously and periodically accelerated electrons and the periodic impact of polarised photons on a receiver can be measured. Here one can speak of an EM wave.

For more in-depth information, please read this.