Can light be focused with an externally applied field?

Is this possible? Can a E&M wave be controlled in a meaningful way by an electric and/or magnetic field?

I know that charged particles are acted upon by these fields, that’s how particle accelerators work, but what about applied to camera lenses or other optical systems? In essence, why are we using glass and mirrors to interact with light, why not devices that generate fields?

I also think this is different but related to a waveguide, which does modify how the light propagates in a fundamentally different way than glass, but its based on boundary conditions not an externally applied field.

I guess my first thought is that the answer is no because the fields would not coherently interact, but I am interested if other people have experience with this!

Hello, Isaac.

As you already wrote, the transmission material (any interactable medium) is essential for this. In the vacuum, the light can be propagated and only the gravitation (distortion of the space) can change the light propagation.
In a more practical way, we used to use an acoustics optical modulator which uses the medium can change prorogation mode in the material.
Returning your question, there is ‘Kerr effect’ which used to be adopted in a pulse laser amplifier. The strong E-filed induces the nonlinear optical phenomenon in medium and it changes the index. (it is a really fast transition and called Q-switching). It is not a practical way to replace the lens.

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Thanks for the background and the use-cases for when this effect is applicable! I hadn’t thought about an acoustic optical modulator as a perfect example of modulating the media to induce an optical effect.

The Kerr effect is really cool! Nonlinear optics is not an area I have had much experience with, so the phenomenon associated with it aren’t at the forefront of my mind. Thanks for sharing!