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Scientists drag light by slowing it!

bhank

bhank

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Scientists drag light by slowing it to speed of sound

Not really sure if this has been posted here but I found this very cool. Basically they slowed a green laser by shining it through a ruby rod spun at up to 3000 rpm, causing the light to slow to the speed of sound they say and redirecting the image at an angle up to 5 degrees. The suggested real world applications sound pretty promising to me.

What are your thoughts?
 





That is a cool article I have not seen til now, thanks for posting. Lot of food for thought, really incredible!
 
Thats pretty cool :D

If light can be constantly slowed to the speed of sound. By theory, you would be able to "time travel"
 
Anyone else wondering.....what would this do to pumped and pulsed lasers?
 
The only problem is that the light is slowed down only til it remain inside the crystal, when the photons come out from the other side of the rod, they reacquire their "natural" speed.

That thing about slowing down the light in air, is one of the dreams of all scentists (and weapon makers :p) ..... consider that the power of a laser is expressed in W/s, at light speed ..... if you can, as example, slow down the light 1000 times, the resulting power is ofcourse 1000 times higher, on the target .....

Just imagine ..... 445nm 1KW handheld laser pointer powered from a 18650 battery :p :D (who cares if the output light only travel to 300 Km/s ? ..... it will be a hell of a burner :crackup:)
 
Bah, speed of sound is so last decade. How about the speed of a moped?

HIMNL9 said:
if you can, as example, slow down the light 1000 times, the resulting power is ofcourse 1000 times higher, on the target
Click to expand...

Free energy: Laser powers solar panel which powers laser

troll_face.png
 
Slowing the speed of light in a ruby rod increasing the potential power of a laser as a weapon ?

So it's easy enough to shoot something with a ruby rod projectile but the part about keeping it spinning seems a bit more difficult.
If it is an organic target (read into that what you will) keeping the target still enough to then aquire the spinning rod with the laser...that would really be a major engineering marvel.

Who wants to try it first ?
 
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I can do MUCH better! I didn't just slow light down, I reversed it completely! Took only one mirror to do...
Slowing light isn't new, any material with a high refractive index effectively slow light. Getting light really slow is interesting, but it's not like time travel will happen.

Transmission through a spinning window slightly rotates the polarization of the light, typically by a microradian. It has been predicted that the same mechanism should also rotate an image. Because this rotary photon drag has a contribution that is inversely proportional to the group velocity, the image rotation is expected to increase in a slow-light medium. Using a ruby window under conditions for coherent population oscillations, we induced an effective group index of about 1 million. The resulting rotation angle was large enough to be observed by the eye. This result shows that rotary photon drag applies to images as well as polarization. The possibility of switching between different rotation states may offer new opportunities for controlled image coding.
Rotary Photon Drag Enhanced by a Slow-Light Medium
Click to expand...
The ruby under special conditions slowed the light, the rotation wasn't part of that but ment to research the light drag.
 
ShortyInCanada said:
Slowing the speed of light in a ruby rod increasing the potential power of a laser as a weapon ?

So it's easy enough to shoot something with a ruby rod projectile but the part about keeping it spinning seems a bit more difficult.
If it is an organic target (read into that what you will) keeping the target still enough to then aquire the spinning rod with the laser...that would really be a major engineering marvel.

Who wants to try it first ?
Click to expand...

No.

First, the spinning part was only for "drag" (or rotate, if you prefer) the path of the light for check how much it slowed, not for slow down it ..... the light slow its own speed when it pass through different mediums, in fact the "speed of light limit" is a constant only in the vacuum, inside different transparent materials, the photons have different speeds, always slower than in the vacuum, and it depend mainly from density and atomic reticular structure of the material ..... it just happens that ruby is a material dense enough to have the ability to slow down the photons that way, but when they come back from the opposite side of the rod, they regain their normal speed in the air.

IF (and it's a big "if" this one :p) there was a way for keep the photons slowed down also when they come out from the rod, then it will increase the transferred power of the beam, cause the transferred power is, basically, photons density for time.
 
I think it's just a matter of perspective though. From the outside the light seems to slow down in the rotating rod, but it doesnt move any slower than it would in a stationary rod. The spinning rod just causes the light to take a very long helical path through the rod (if you imagine the rod as stationary).

I'm not sure why ruby was chosen as the material - i guess it should work with anything of sufficient refractive index, like lead glass or even ordinary glass - perhaps those materials are not mechanically strong enough to withstand the rotation speed.
 
i knew light slowed down when it passed through a clear object, but it never occurred
to me that if you spun it at a high enough speed that you could turn or redirect the
light's direction before it left out the other side.
 
^ well, the photons still travel in linear path INSIDE THE ROD, but the rod is rotating, so when the light come out from the other side, the output point of the rod that is corresponding to the input one have shifted ..... the path is helical in the space, but is linear in the medium.

As easy example, imagine the rod as a bunch of linear tubes all together ..... shoot a ball in one of the tubes (except, ofcourse, the central one, that is the rotation axis :p), and the ball go linearly from one side to the other ..... now rotate the whole assembly and still shoot a ball in one of the tubes, it still travel linearly inside the tube (that is remaining straight), but at the same time is making a helical path respect to the general space, and when it come out from the other side, it's shifted from its original input path.

(simplified a lot, i know, but it's just for give an example ;))
 
HIMNL9 said:
the transferred power is, basically, photons density for time.
Click to expand...
if you slow down speed, you don't increase photons per unit time. If power was increased 1000 times, that's 100,000% efficiency, which puts a 120% efficient laser diode to shame. See post number 6. :can:

If bicyclists in a line traveling at 36kilometers/hour spaced 10 meters from each other, they would hit a wall at the rate of one every second.

If they were to all slow down to 18kilometers/hour when they crossed a line a 100 meters before the wall, they would be spaced 5 meters apart instead, and they would still hit the wall at a rate of one every second.

What am I missing? :confused:
 
^ only the fact that you are still pumping in the rod the photons at light speed, and that we are speaking about 2 different parameters, intrinsic energy and energy density :p

Let me try to explain:

assume, absurdly (remember, it's just an example), that you are pumping in the photons at light speed, and that they are spaced at 1 meter each one, so you have 1000 of them each Km, and light speed is 300000Km/s ..... this means, 300000000 photons each second ..... each photon have its own energy, that depend from the wavelenght, NOT from the speed, so, say that those 300000000 photons each second are 1W of energy of the beam, and that DENSITY of 1 photon per meter is 1W of power.

Now, you pump them in a device that slow down them 1000 times, and for do this it also "pack" them 1000 times closer, so at the output they are 1000 times slower than at the input, and, for this, they are also 1000 times closer one to the other ..... this means that at the exit, also if your beam have still an intrinsic INPUT energy of 1W, now at the output you have 1000 photons each meter, not 1 as before, so the intrinsic energy of the output beam (considered as photons per time unit) is 1W, where instead its energy DENSITY is now 1000 times higher.

Photons are bad beasts ..... opposite to phisical objects, they feel funny to cause some paradox, sometimes ;)
 
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