DavidWhalley94 via Twitter asked:
If you shone two lasers directly into each other, what would happen?
We put this question to Dr Graeme Hirst, from the STFC's Central Laser Facility...
Graeme - Well that’s a good question. If you shone them directly into one another, then you're quite likely to break the lasers unfortunately. But if you imagine you're going to misalign them slightly so that the beams crossed, but they don't go down the throat of the opposing laser, then if you were to do that in a vacuum, if you just have one light beam crossing another then to all intents and purposes, nothing happens. Once you get to extreme physics conditions where the laser intensity does become spectacular - and in some experiments we do, we’re getting there - you might imagine that you can perturb the vacuum. You can change the vacuum with the intensity of light you need. But mostly, this is interesting if you cross the two beams over in some kind of material, and if you do that, you can achieve all sorts of interesting effects in the material by combining two laser beams, through the properties of the material.
Well, i do believe a percentage of that energy will manifest to actual matter given by the formula E=Mc^2. We have shot many beams of photons at each other, and this is an experimental fact. Many of the photons will not collide though, and just continue on, falling into the same state as the partner photons that surround them. Mr. Scientist, Tue, 1st Dec 2009
It depends on the degree of coherence between them if they are of the same single frequency they will form an interference pattern where they reinforce and cancel each other.
In the absence of any other material light beams do not interact in any other way than to produce localised interference based power density variations. Soul Surfer, Sun, 6th Dec 2009
Light doesn't seem to influence light electromagnetically, strange isn't it. One way to look at it is to say that Bosons " Bosons (such as photons) do not notice each other and can be at the same location at the same time without any problem. That's why different rays of light can cross each other without any problem and continue to go straight ahead as if nothing happened. Because bosons do not notice each other, it is very difficult to build a stable structure out of bosons."Here
The experiment was done at the Stanford linear accelerator in 1997. The collision was between a laser beam of 6 X 10 ^14 Hz and a gamma ray of 10^25 Hz which produced an electron anti-electron pair. That would suggest the collision energy would have to at least equal, M = fh/C^2. Ron Hughes, Mon, 28th Dec 2009
If photons do not interact then how do we explain the above experiment? It would appear that we do not understand the photon. One of the problems is how we have pictured the photon graphically. Since the late eighteen hundreds we always describe the photon with a mathematical representation which is the sine wave. When I visualize light going through a polarizing grating I see a sine wave entering the grating at one angle and coming out the other side shifted by ninety degrees. That is a picture of what happens but obviously does not truly represent the truth. Ron Hughes, Mon, 28th Dec 2009
A single photon is not a wave? Please enlighten us and describe a single photon. Ron Hughes, Mon, 28th Dec 2009
I haven't come across a really concise non-technical description of a photon. In essence, a photon is the smallest excitation of the free electromagnetic field. You use them to describe the interaction between matter and the electromagnetic field. Matter can interact with the electromagnetic field to either generate or absorb photons. The classical sine-wave you would find coming from a laser, for example, is a particular way of "stacking" photons known as a coherent mode. These coherent modes behave like the classical light described by Maxwell's equations.
Geezer, you could say that, but I'd be a bit nervous about the description of a photon as being the smallest detectable excitation of an EM field simply because quantum mechanics is all about observations/detections. If it's the smallest unit of the field we can observe, does it make any sense to talk about smaller units of the field? jpetruccelli, Mon, 28th Dec 2009
As always JP
This already happens inside a laser resonance cavity (= inside the laser).
Interesting topic but while discussing the interaction and noninteraction of photons, please don't forget the Hanbury, Brown, and Twist effect, or bunching of photons. sciconoclast, Thu, 17th Jun 2010
Well what about when 2 weak unseeable Laser lights interact will that area of Interaktion be Seen? Please explain for Kids? Markus Baumgartner, Fri, 28th Mar 2014