# Wave amplification?

mjasin
I am familiar with the idea of amplitude increases that can be produced by waves that are "in phase". I can imagine this easily with sound or water. I have 2 questions with regard to EM radiation:

1) Do the same principles apply with light/EM radiation? What does "in phase" mean on a practical level for say visible light?

2) If two light/EM sources are put at right angles to each other such that the beams intersect, what sort of interactions/amplifications might you get?

I realize these may be huge questions, so feel free to tell me to find a physics prof to sit down for coffee with. :)

THanks

Absolutely, bright spots on an interferance pattern are points where the light from multiple sources are in phase.

If you take two coherent light sources, you will get an interferance pattern if you intersect them. If you intersect two incoherent sources, you will just get a spot of higher intensity (more correctly, irradiance) where the beams intersect.

I should point out that increasing irradiance in this fashion is not regarded as amplification.

Claude.

mjasin
Thanks for the response. Your answers have created more questions for me.

1) Does the principle of coherence apply to sources other than lasers? Could you have an x-ray source that emits coherent xrays?

2) Does the intersection of two non-coherent sources produce altered wavelengths? Or, is the irradiance a simple additive phenomenon?

Thanks again!

1. Coherence applies to any coherent e/m source. Lasers are but one example of a coherent source. I'm not sure if there are coherent x-ray sources available, perhaps another forum member may be able to answer that.

2. Irradiance is by and large an additive phenomenon, although there are special cases where it may not be, for example, in optically non-linear media.

Non-linear effects can cause new wavelengths to be generated, although in order for this to happen, the two beams are typically coaxial, rather than perpendicular to one another.

For the vast majority of cases though, particularly for low powers, no new wavelengths will be generated.

Claude.

Gold Member
Claude Bile said:
I'm not sure if there are coherent x-ray sources available, perhaps another forum member may be able to answer that.
Wasn't that idiot Bush trying to use frequency-shifting of an ultraviolet laser after coherence was obtained, for deployment in the Star Wars project? I know that the programme as a whole was a joke, but that approach seemed to show some promise for high-frequency lasers.
As a side note, I needed a gamma laser for my book. That's not exactly attainable, of course, since gamma won't bounce. My approach, which I would love to have some criticism of, was to build a quartz ring with 2 liquid crystal windows of equal refractive index to the quartz replacing 2 facets. One was open to a tube of neon 21, which in turn was exposed to a U-238 pile. That should result in gamma photons of somewhat over 1.6GEv, if I read things correctly. Although gamma can't be reflected, it will refract in a quartz lattice. My idea was to keep pumping photons into the ring in the same direction until you have enough to cause some damage (ie: synchrotron the **** out of it), then polarize the second window to let it out. Steering and focusing were to be achieved by electrostatic deflection plates.
(I can see Russ having a tonne of fun with this.)

Claude Bile said:
I'm not sure if there are coherent x-ray sources available, perhaps another forum member may be able to answer that.

At least down to 80nm is achieved:
http://www-hasylab.desy.de/facility/fel/main.htm

An 0.1nm XFEL is planned to start running in 2012 at DESY:
http://xfel.desy.de/technicalinformation/photonbeamparameter/index_eng.html

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pallidin
Danger said:
Wasn't that idiot Bush trying to use frequency-shifting of an ultraviolet laser after coherence was obtained, for deployment in the Star Wars project? I know that the programme as a whole was a joke, but that approach seemed to show some promise for high-frequency lasers.
As a side note, I needed a gamma laser for my book. That's not exactly attainable, of course, since gamma won't bounce. My approach, which I would love to have some criticism of, was to build a quartz ring with 2 liquid crystal windows of equal refractive index to the quartz replacing 2 facets. One was open to a tube of neon 21, which in turn was exposed to a U-238 pile. That should result in gamma photons of somewhat over 1.6GEv, if I read things correctly. Although gamma can't be reflected, it will refract in a quartz lattice. My idea was to keep pumping photons into the ring in the same direction until you have enough to cause some damage (ie: synchrotron the **** out of it), then polarize the second window to let it out. Steering and focusing were to be achieved by electrostatic deflection plates.
(I can see Russ having a tonne of fun with this.)

Perhaps, but I do not readily see how coherence is achieved in this scheme.

Gold Member
pallidin said:
Perhaps, but I do not readily see how coherence is achieved in this scheme.
That's why I don't call it a laser. I was hoping that the energy density might be high enough just with focusing.

pallidin
Danger said:
That's why I don't call it a laser. I was hoping that the energy density might be high enough just with focusing.

In that case, yes, it is possible, but how "high" you go is dependent on material constraints. And those constraints are extremely difficult to deal with.

Gold Member
Yeah, I hadn't thought of that. I don't imagine that optically matching the LC windows to the quartz would be a tonne of fun either. Oh well... it's just an SF novel.