# Is it possible to divert light and/or wave by light or wave?

Is there a way to divert (deviate, deflect) light (photons) by another light (such as laser) or wave? Just like what a prism can do but using a ray of light or wave instead of a prism.

Maybe I'm searching all possible ways to divert light and radio waves. Although for me, it's interesting to find ways in which they do not need a solid or liquid object. Such as magnetic field, light and... Specially the ways that we can implement them today in a lab.

Note: Some information like cost of implementation, accuracy in the deviation, limitations of the method and something like these about each method can be useful too.

Note: Also diverting the radio waves by different methods is questionable here.

• There are many, many ways to "divert" light. Magnetic fields are used in isolators to rotate the polarization of light so that it only travels one way through the isolator. And electro-optic devices uses ultrasound to do all sorts of things, such as diffract, modulate or reflect light. Optical switches (Pockels and Kerr cells). It really hard to be more specific unless we know what you mean by divert, or what your potential application is. – JohnS Apr 17 '18 at 23:15
• @JohnScales Note the OP says "in which they do not need a solid or liquid object" – garyp Apr 17 '18 at 23:52
• Thank you @John Scales for your reply. I added a picture to my question to explain divert word (Deviate) in my question and other assumptions of the problem and want know are there any accurate ways to do it? – RAM Apr 17 '18 at 23:56
• @garyp He says: "I'm searching all possible ways to divert light and radio waves. Although for me, it's interesting to find ways in which they do not need a solid or liquid object." All possible ways. The idea of dispensing with solids or liquids is clearly a secondary concern. – JohnS Apr 18 '18 at 0:15
• I don't know of any method that does what you want in free space. The standard methods in electro-optics all use crystals or liquids. Brillouin scattering is a standard method whereby standing waves in a transparent crystal create a diffraction grating via the variations in index created by ultrasound. Electro-optics devices are pretty common if one would suit your application but these all require solids or liquids as far as I know. I suppose you could great standing waves in air between two transducers, but without doing the calculation, I can't say if this is feasible. – JohnS Apr 18 '18 at 0:32

OK, I'll go out on a limb here and say that you might be able to create a suitable diffraction grating in air between two ultrasonic transducers. It is certainly possible to produce pretty intense sound this way. The standing waves of sound will produce a sinusoidal variation in the index through which your laser passes. But I would have to do some more thinking to see if the effects would be readily visible. Ultrasonic transducers are pretty inexpensive compared to EO gear. You would shoot the laser through the gap between the transducers at some angle (so as to not hit the transducers). It might work.

• Thank you @JohnScales for your answer and your explanation about it. I'm very cautious about my question and I want to figure out whether the way your offer is working in space or does it need to the atmosphere? Probably the implementation of a solution outside the atmosphere be a better option for my idea and question, although its creation in the atmosphere is also significant in the second phase. If there is some way for me to know about your way please direct me to it. – RAM Apr 18 '18 at 1:04
• The ultrasound idea requires air as a medium for the standing waves of the index of refraction. So absolutely will not work in vacuum. If that is the case I think the final answer is no. – JohnS Apr 18 '18 at 1:11
• John, I have thought about my idea in vacuum but top side (inside) of atmosphere can be in this case. So if you think your idea is possible to test in a lab, so may you calculate it as theory? – RAM Apr 20 '18 at 1:25
• @RAM This is worked out in Morse and Ingard's theoretical acoustics. I'm working from memory here, but as I recall that they work out the fractional change in refractive index in terms of the sound pressure. Then you just need to figure out the sound pressure levels produced by your ultrasonic transducers. You can generate SPL's on the order of 150 dB at 20 kHz without anything exotic. The only trick is to remember that air coupled transducers act as a capacitive load. So impedance matching is important to keep from just heating up your transducers. Hope this helps. Cheers, J. – JohnS Apr 21 '18 at 16:41

The answer to the question in the title of the post, clarified by your picture, is, probably, no.

This answer addresses the case where no solid or liquid objects are used, which seem to be interested to understand.

If a light beam or a radio wave propagate in a uniform linear medium like vacuum or, to a large extent, air, another light beam or radio wave can affect it only where the waves overlap, via the interference, but not before or after.

This, of course, follows from a principle of superposition which states, using a quote from Wikipedia, that "... for all linear systems, the net response caused by two or more stimuli is the sum of the responses that would have been caused by each stimulus individually".

Applying this principle to the picture in your post, we can say that the path of the blue beam, after its intersection with the interfering red beam, would not be changed by the red beam, because the red beam is not present in that region and, therefore, the sum of the blue beam and the red beam in that region will be defined (equal) to the blue beam alone.

In a vacuum, electromagnetic waves pass right through each other with zero interaction. That is a very well established fact, both experimentally and theoretically. @John Scales is right that in air it is possible to form a diffraction grating, and deflect light, using acoustic interference.

But it appears that you want one type of electromagnetic wave to deflect another type of electromagnetic wave. It can still be done (in a gas, solid, or liquid), but isn't simple. For example, a very powerful laser pulse can be used to form what amounts to a transient diffraction grating in air, resulting from local heating of the air along the maxima of an interference pattern. That diffraction grating can momentarily deflect another laser beam.

Some information like cost of implementation, accuracy in the deviation, limitations of the method and something like these about each method can be useful too.

Implementing would be very expensive and cumbersome. Accuracy of deviation could be very good. The system would consume a lot of power.

To do the same with radio waves would be extremely difficult. Maybe theoretically possible, but very difficult.

• Thank you for your answer, Yes I want something to deflect light or wave by it and should not be solid or liquid. So I thought to another wave or light like laser but on the other hand it must be testable and possible to implement in large scales too. I think if it was testable and can be implement it on the earth and as you said accuracy of deviation could be very good then cost of it can be in a lower levels of Importance. I welcome any ideas on this subject. – RAM Apr 18 '18 at 1:27
• "In a vacuum, electromagnetic waves pass right through each other with zero interaction. " I would qualify this , see my answer here physics.stackexchange.com/questions/399846/… . maybe for "visible freqencies and lower" – anna v Apr 18 '18 at 4:19
• I know inverse particle/antiparticle annihilation is theoretically possible in a vacuum, but has it been observed? Maybe there is another route I'm not aware of? – S. McGrew Apr 18 '18 at 5:15
• If you know of experiments that have demonstrated photon/photon interaction in a vacuum, please post a link to the relevant papers. – S. McGrew Apr 18 '18 at 5:24
• The vacuum in the particle beams is quite adequate for interactions to happen singly. Virtual particles are mathematical entitities, and the flux of particles very seldom has interactions in the same volume of h_bar for beam particles to affect each other. LEP had the inverse, e+e- annihilation in vacuum. They are proposing gamma gamma colliders indico.ihep.ac.cn//event/6030 – anna v Apr 18 '18 at 14:58

The answer is no, for visible frequencies and lower, the photon photon interaction is negligible, and therefore the light beams which are emergent from zillions of photons cannot scatter as in your diagram. They go through each other in a superposition. See my answer here.

Superposition means that interference patterns in space can appear as seen in this MIT video given the appropriate conditions . Superposition does not transfer energy from one beam to the other, just reorganizes it in space in the overlap region.

In principle, you could construct a high energy (short wavelength) laser where each photon would convert to an electron and an anti-electron in vacuum, then the second light beam would scatter off the electron and/or anti-electron.

As the previous answer mentions that Photon-photon interactions in vacuum can happen the cross-section is quite small.

• Thank you JQK, You have written "in principle", so is it testable in lab? What are limitations of this way? – RAM Apr 19 '18 at 11:02
• I found a related research Here. – RAM Apr 19 '18 at 11:34
• There were results from SLAC in the 1990s that demonstrated via nonlinear QED photon-photon scattering directly. – JQK Apr 19 '18 at 21:43
• JQK, you wrote about electrons. As I said in my question, I just want prevent using a liquid or solid thing to deflect light (specially in vacuum else in atmosphere) then I have not any problem with throwing the electrons to the photons instead of red beam in the picture in my question. Now do you think is it (light deflecting with high accuracy) possible if we throwing the electrons in a special angle to it? – RAM Apr 20 '18 at 1:40