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ArcticMyst Security by Avery

Gas Laser Travelling at Near c?

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So interesting question just popped in my mind....

What would happen if a laser (be it gas, whatever) was travelling at near light speed? Assuming doppler effects are not noticed, what would happen? The cavity of the laser would shrink, so would that affect the wavelength that it emitted? I would think that, because the cavity would be shorter, it would diverge more? But what else would happen?

Obviously, this lasers is travelling at this speed parallel to its emission axis.
 





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It would fail to lase as it reached C because the photons would no longer be moving in relation to the cavity, and thus no photons would be interacting with the mirrors or gain medium.
 
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The photons would have to be moving in the cavity at the speed of light, so it would have to lase. That's relativity, right there.
 
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I think the blue or redshift from the doppler effect would be much more significant than the effect from the shrinking of the cavity...
 

AUS

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It depends on your field of reference- you would see different things depending on weather you were travelling at the same speed as the device or if it was moving towards or away from you. As Einstein showed, it is relative to the observer.
 
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If the cavity is moving at C and the photons are moving at C they remain in place relative to the cavity (light-speed observer). Lasing is when light is amplified by reflecting within the cavity, not simply having photons in the cavity. If the cavity is sub-C then yes, lasing would still occur.
 

Lase

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If the cavity is moving at C and the photons are moving at C they remain in place relative to the cavity (light-speed observer). Lasing is when light is amplified by reflecting within the cavity, not simply having photons in the cavity. If the cavity is sub-C then yes, lasing would still occur.

Ok so, hypothetically, if it were a pointer and not a gas laser and it was travelling just sub-C (assuming you could keep up and view it) would the beam only be as long as the difference between the speed of the pointer and C?

Lase
 
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Yeah, that sounds about right to me. Fractions of C are still pretty significant though, so you'd still see it shooting out pretty fast/far. It would probably look like Star Wars laser effects, which move slowly to the target, lol.
 

AUS

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The speed of light is constant, relative to the observer.

If you were keeping up with it then it would behave exactly the same as if you were seeing it here on earth. If you and the laser were both traveling at 90% of C, Relative to you, the laser would still appear go at the speed of light. For you, time would slow down so it always appeared to be travelling at C.

That's how relativity differs from Newtonian physics. You will always observe the laser going at the speed of light no matter where you observe it from. Therefore, as Eisenstein figured, time must change for the different observers, not the speed of light.
 
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The speed of light is constant, relative to the observer.

If you were keeping up with it then it would behave exactly the same as if you were seeing it here on earth. If you and the laser were both traveling at 90% of C, Relative to you, the laser would still appear go at the speed of light. For you, time would slow down so it always appeared to be travelling at C.

That's how relativity differs from Newtonian physics. You will always observe the laser going at the speed of light no matter where you observe it from. Therefore, as Eisenstein figured, time must change for the different observers, not the speed of light.

Well said, c is constant for every observer.
 
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Right! I forgot about time dilation. Assuming you were observing from outside of the time-space continuum you'd see the light move slower =P.
 

Blord

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You are talking about extra dimensions. Maybe the relativity theory don't apply in those dimensions. Anything could happens there. Like the worm-hole that take short cuts in the path.
That would be nice. Hopping to a star many lightyears away in just a few hours.
 
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But no one has answered my question! What is the result from a shortened cavity?
 
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If the cavity is moving at C and the photons are moving at C they remain in place relative to the cavity (light-speed observer). Lasing is when light is amplified by reflecting within the cavity, not simply having photons in the cavity. If the cavity is sub-C then yes, lasing would still occur.

I once brought up a similar question in my high school astronomy class. Whether the object producing light's speed would have an effect on the speed of the light it produces. The answer? No. It will always travel at the same speed not relative to it's surroundings. I will travel that speed + the speed of its cavity. Strange stuff. However, I did not follow up with if the cavity was also traveling at C. So who knows.

PS. I've been watching Ereuka nonstop for 3 days. Started season 3 last night. Pretty sure my brain is strictly wired to theoretical physics now, I would take what I jus said with a grain of salt.
 
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Maybe it will mode-hop at different speeds. I think just because the cavity is some multiple of a wavelength, the gain material still has to be able to absorb and emit that wavelength too for it to lase. So I think for a gas laser, the most efficient line will change as the cavity length changes. It's Friday, though, not a thinking day.
 




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