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How does one slow down the travel path of light?

wouterjesse

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Hi there,

When learning about total internal reflection for a light installation I am working on.
I notice that the speed of light is slowed down when shining through transparent materials.
I know this is how light behaves but never seen light behave as slow as in this video.
See the demonstration from 0:28s

Now I am wondering if there are transparent materials which I can use to slow down light in such a way that it is very noticeable?
And are there other methods to slow down the speed of light to make it more noticeable?
 





Eidetical

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I believe light can be slowed down to a complete stop, but not in a way that can be viewed by the naked eye. Physicists here can explain better. There are ways to observe light interact with physical things, such as "light-in-flight" holography invented by Nils Abramson in the '70s.
 
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I'm not totally understanding your question.

Do you mean slowing the speed down to a point where you can observe the difference in speed indirectly or directly? Because of lights fast speed there won't be any way to slow the speed down to a point of it being visible. There are some experiments that have been done in lab experiments where they have stopped light, and slowed it down to <20mph with a Bose-Einstein condensate, but none of those experiments are attainable to us. Most optical materials have an index of 1-2, so few with half the speed of light.

Now if you are talking about experiments that use effects related to the slowing of light, than there are many.
 
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I was going to mention the Bose Einstein condensate, but Matt beat me to it. :LOL:
 
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Ridiculous paul, OP was asking about transparent materials he could use to slow down light, the Bose Einstein condensate is hardly useful as it occurs at virtually absolute zero temp, not practical at all.
 

CurtisOliver

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Ridiculous paul, OP was asking about transparent materials he could use to slow down light, the Bose Einstein condensate is hardly useful as it occurs at virtually absolute zero temp, not practical at all.
Well I was going to suggest a black hole but I guess not. Black against the black of space could be transparent right?
 
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julianthedragon

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I know this is how light behaves but never seen light behave as slow as in this video.
Where is the light behaving slowly? If you're talking about when he shines the green laser through the clear tubes, I believe the visual effect is merely the laser taking a few seconds to reach its full power, not the actual light taking its time to make it across
 

CurtisOliver

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Where is the light behaving slowly? If you're talking about when he shines the green laser through the clear tubes, I believe the visual effect is merely the laser taking a few seconds to reach its full power, not the actual light taking its time to make it across
Yes, precisely. This isn’t the speed of the light at all.
 

kecked

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In theory if you had a long enough path length and split a beam prior to the slower media you could see first the light then the slowed light. You’d probably need a light years distance to make it work. I mean even if you slow it by 50% that time difference would be hard to measure. You can however experience this with radio waves whe you hear an echo. You hear it on cell phones from time to time. It can be done with a bridge bucket delay. There are ways.
 

Eidetical

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The speed of light is an obvious factor to consider when making holograms with pulsed lasers. Usually when making holograms, the laser beam is split for reference beam and object beam paths. The length of the two paths are often equalized to the accuracy of the coherence length of the laser's light. Pulsed lasers for holography typically include an etalon which gives huge coherence length to the light, and usually have a pulse length of about 35ns. That's about a meter long pulse of light. The beams need to be equalized to ensure that both arrive at the recording plate at the same time. The path lengths for the master hologram for a portrait like the one below (from 1994) is typically many meters long. The 32x43cm master for "Sherry" was shot by Positive Light Holographics with a frequency doubled pulsed Nd:YLF laser with an output of about 750mJ at 527nm. The 32x43cm transfer was done by me with a 35mW Spectra-Physics model 907 He-Ne at 633nm.

Sherry 2.jpg
 
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Light in a vacuum travels at C. Light passing through a transparent material travels less than C.

This is how you slow the speed of light. Video it at 10 trillion FPS.
 
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I think there is a little bit of confusion in this thread.

1. Materials with very high refractive indices will slow light (by absorbing and re-emitting photons). A refractive index of 2 is very high. 4 is extremely high. A refractive index of 4 would correspond to light moving at 1/4 of the speed, which is still 7.5 x 10^7 m/s, obviously too fast to observe a noticeable distance at scales the size of a classroom.
2. It is possible to slow the group velocity of a wave packet much more than this, but observing such a phenomenon would have to be done indirectly. A phase velocity of zero or greater than c does not mean light never comes out or comes out before it went into the material, it just means that wave packets behave very strangely.
3. You could build an apparatus to show slowing of light in a classroom or household, but it would have to be indirect and you'd have to spend some time explaining how what people are seeing is actually slowing down of light.
 

Eidetical

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Ultrashort laser pulses are used in the video above and with the "light-in-flight" technique described below, but ultrashort coherence length is also appropriate with the latter. I'd bet that modern high powered diode lasers with short coherence length could be used to make such a hologram at home. The first experiments were done with a Spectra-Physics model 170 argon ion laser at 514nm with no etalon, giving 2W with a few centimeters of coherence length.

 
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Ridiculous paul, OP was asking about transparent materials he could use to slow down light, the Bose Einstein condensate is hardly useful as it occurs at virtually absolute zero temp, not practical at all.

If you saw the thread title explaining how the Bose Einstein condensate stops light, though not useful to the OP, is pertinent. Why is everything I say ridiculous? I guess I'll start calling your statements out. :(
 
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If you saw the thread title explaining how the Bose Einstein condensate stops light, though not useful to the OP, is pertinent. Why is everything I say ridiculous? I guess I'll start calling your statements out. :(

Not only was your posting useless for the OP, but it was already mentioned as a related point of interest by someone else, you wasted a post just to draw attention to yourself without adding any useful content what so ever.

You were basically saying " Look at me, I have nothing of value to add but I could have said that too. " .

If you had added anything of interest what so ever I wouldn't have said anything.......but basically all you said was " Look at me and how smart I think I am. " and now you vow to be confrontational out of spite. :(
 




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