As an electromagnetic radiation phenomenon, it’s perhaps not so surprising that light is affected by a magnetic field. This Faraday effect (FE) has been used since its discovery by [Michael Faraday] in 1845 for a wide range of applications, allowing for the manipulation of light’s polarization, something which is very useful in the field of optics, for remote sensing and spintronics. Despite this being such a well-known property of EM radiation a recent study claims to have made a new discovery here, with what they claim is about the ‘optical magnetic field’.
Their central claim is that it is not just the electrical component that contributes to the FE, but also the magnetic one, due to Zeeman energy that expresses itself from the magnetic component as a form of inverse FE. Based on their experimental findings they estimate that it contributes to the final measured FE by about 17% at a wavelength of 800 nm.
While definitely a very niche physics paper, and with no immediate implications, if independently confirmed it could deepen our understanding of the Faraday effect, and how to use it in future technologies.
“As an electromagnetic radiation phenomenon, it’s perhaps not so surprising that light is affected by a magnetic field.” Huh, that’s news to me. Might want to read up about it a bit more.
Faraday effect (magneto-optical rotation): When polarized light passes through certain materials (e.g., glass or crystals) in a magnetic field aligned with the light’s direction, the polarization plane rotates. This is due to the magnetic field affecting the material’s electrons, causing circular birefringence (different speeds for left- and right-circularly polarized light). Recent research (as of late 2025) has shown the light’s own magnetic field also plays a subtle role, challenging 180-year-old assumptions, but the primary effect is still via the medium.
For those of you working with high voltages, the Faraday effect makes a very nice contact-less voltage measurement system.
IIRC acrylic has a fairly large Faraday effect. Run a piece of acrylic beside a high voltage conductor and shine polarized light through it – the polarization will change in proportion to the voltage in the conductor.
It’s also stupid high bandwidth: well into the 10s of GHz.
The sensitive element can be very tiny, which makes it a good (but not very sensitive) probe to put on the end of a fiber and poke around inside high power RF amplifiers to see where the electric fields are, without perturbing things with (e.g.) a capacitive probe.
I know where the on-off switch to the TV is and I’ve heard tell of radio and physics. Which might explain the question: “Did you really mean to say ‘bandwidth’ up there?”
Yes. What do you think I should have called it?
I don’t know what you’re naming. It the word has two different definitions in two different fields, in yours it seems to be “is the frequency high or low?” Thank you.
The transducer accurately converts an oscillating electric field to a modulated light signal over a bandwidth from near DC to more than 40 GHz.
What other meanings of bandwidth might be confusing here?
Great tip!
Yea a good tangible example of this is the Faraday Rotater. That said, I think I have to read the paper here. The description given here keeps having me think “didn’t we already know that?”. So I’m missing something basic.
The “Missing” Magnetic Contribution
Old Knowledge: Since Michael Faraday’s discovery, it was assumed that the rotation of light’s polarization (the Faraday Effect) was caused by the electric field of light interacting with the electric charges (electrons) in a material. The magnetic component of the light wave was considered too weak to have any measurable impact.
The New Discovery: Researchers at the Hebrew University of Jerusalem showed that the oscillating magnetic field of light actually exerts a “magnetic torque” on the atomic spins within a material. This is not a negligible side effect; it is a “first-order” effect that directly causes polarization rotation.
Why This Matters
This isn’t just a theoretical correction; it has practical implications for future technology:
Spintronics & Memory: Understanding that light can “talk” to matter magnetically allows for more precise control over magnetic memory and data storage using light.
Quantum Computing: It provides a new mechanism for controlling “spins” (the basis for many qubits) using optical pulses.
Optical Engineering: Engineers designing sensors or isolators (which prevent light from back-reflecting in lasers) now have a more accurate “blueprint” for how materials will behave, especially in the infrared spectrum used in telecommunications.
In short, the paper proves that light doesn’t just illuminate matter; it magnetically influences it in a way we’ve been ignoring for nearly two centuries
I just want to say that’s a fantastic recap and comparison, thank you!
Been wondering and waiting for people smarter than me to elucidate this paper, thanks for socializing it! New fundamental stuff is so neat.
Another way light (rather, the production thereof) is affected by magnetic fields:
https://www.youtube.com/watch?v=GxXl8zQIIZI
Gravitons and light may have an interaction
https://m.youtube.com/watch?v=qXwpplJCbWU
https://phys.org/news/2026-01-quantum-gravity-dimensions.html
https://spacefed.com/physics/unified-field-theory-solved/