Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



Laser Pointer Store

super high speed camera and laser ????

Joined
Dec 26, 2007
Messages
6,333
Likes
161
Points
0
jamilm9 said:
shine the light through thick glass to slow it down
(sorry to digress)
but i always wanted to know
when i shone my laser onto a pool (filled with water..of course), no matter what angle i shone it into it, the angle in which you saw the beam wouldnt dramatically change.
i.e.
i shone it at like 4° from the ground and the angle on the swimming pool was around 75°

WHY

 

chido

New member
Joined
Dec 4, 2007
Messages
1,918
Likes
0
Points
0
FrothyChimp said:
Light always speeds up and slows down but it never exceeds the 300,000 Km/s limit. Anytime light is not in a vacuum it is traveling slower than the speed of light. Photons will impact and be absorbed by atoms and molecules which then release them again a process which takes a finite amount of time determined by the material. I understand they have used aerogels to slow light to a crawl. But once it leaves the aerogel it's back up to speed near the speed of light.
I'm guessing something like this right?

[media]http://www.youtube.com/watch?v=O3cmbDJEzu0[/media]

And can anyone tell me if the green photon in this "time travel video" is just an animation or if they actually slowed it down?

[media]http://www.youtube.com/watch?v=V7vpw4AH8QQ&feature=related[/media]
 

daguin

New member
Joined
Mar 29, 2008
Messages
16,636
Likes
622
Points
0
nikokapo said:
(sorry to digress)
but i always wanted to know
when i shone my laser onto a pool (filled with water..of course), no matter what angle i shone it into it, the angle in which you saw the beam wouldnt dramatically change.
i.e.
i shone it at like 4° from the ground and the angle on the swimming pool was around 75°

WHY
Light travels at a different speed through water. When the light slows down the object appears to "bend" because you are perceiving it at a different angle. The difference between the two is refraction. The refractive index illustrates the degree of difference between the two materials.

Peace,
dave
 

Switch

New member
Joined
Dec 9, 2007
Messages
3,327
Likes
4
Points
0
GooeyGus said:
And can anyone tell me if the green photon in this "time travel video" is just an animation or if they actually slowed it down?
Its animated   ;)
Duh, a green photon doesn't emit gazillions of other green photons so you can see it.You couldn't see it even if it hit you right in the retina. :p It's just a really really tiny quantity of light.
And a light clock wouldn't really work like that.If you moved it to the left while the photon was in the middle , the photon would simply escape the clock and continue in it's direction. :-/
 

sk8er4514

New member
Joined
Feb 28, 2008
Messages
1,809
Likes
36
Points
0
true. this is a very interesting topic.

on the speed of light: we can create nano particles which create a medium in which the speed of light in the medium is greater than the speed of light, this is how we create invisibility, with a medium n less than 1. n is defined as velocity of light in vacuum over velocity of light in medium, so for the material to be totally invisible the speed of light in the vacuum is infinity. crazy? yes. but in a microwave where the wavelength is in the centimeter range it is possible to have materials which perform as a true invisible cloak, similar to the invisible cloak in harry potter but it wouldn't' work if you were moving around.

http://en.wikipedia.org/wiki/Cloak_of_invisibility#Cloaks_of_invisibility_in_science
 

Switch

New member
Joined
Dec 9, 2007
Messages
3,327
Likes
4
Points
0
Yea but our eyes don't really pick up microwaves anyway.Besides it would be an invisible thingy but you couldn't put it over your head and be invisible.Only the cloak would be invisible, you would still be pretty much visible through it :p Only way to make something opaque to be invisible is eighter to make light go through it or around it.
Check these out, I know it's kinda off topic but I think they're frickin amazing.I can't believe this technology has got this far already.I wonder what kind of cloaking the military has. :-/

http://theblogjoint.com/2006/07/03/invisibility-cloaks-video/
 

diachi

Well-known member
Joined
Feb 22, 2008
Messages
9,447
Likes
1,322
Points
113
Thats right because no light would be reflected back into your eye so you would not see it, its almost like radar invisble aircraft
 
Joined
Aug 15, 2007
Messages
1,880
Likes
3
Points
0
Switch said:
[quote author=GooeyGus link=1209487097/15#21 date=1209547749]
And can anyone tell me if the green photon in this "time travel video" is just an animation or if they actually slowed it down?
Its animated ;)
Duh, a green photon doesn't emit gazillions of other green photons so you can see it.You couldn't see it even if it hit you right in the retina. :p It's just a really really tiny quantity of light.
And a light clock wouldn't really work like that.If you moved it to the left while the photon was in the middle , the photon would simply escape the clock and continue in it's direction. :-/[/quote]

Actually, it's been proven that in a 100% dark room you have a 50% chance of seeing an individual photon. The eye can do some amazing things. You know laser 'speckle"? I'm sure you do... That's nanometre-sized interference patterns resulting from the waves of laser light being slightly out of phase due to irregularities in the surface. The tiny tiny black dots are where a wave peak and trough line up, and teh space in between is where either peak and peak line up or somewhere in between.
Eyes are pretty damn cool... take care of them.
 
Joined
Aug 15, 2007
Messages
1,880
Likes
3
Points
0
And I know a bit about negative refractive materials in the microwave range. A design I've seen uses a lattice of circuitboards essentially, with centimetre size spaces and tracks that make horseshoe shapes on two planes, I think the way it works is that the microwaves create circular electron flows and magnetic fields in the material.
 
L

likewhat

Guest
sk8er4514 said:
true. this is a very interesting topic.

on the speed of light: we can create nano particles which create a medium in which the speed of light in the medium is greater than the speed of light, this is how we create invisibility, with a medium n less than 1. n is defined as velocity of light in vacuum over velocity of light in medium, so for the material to be totally invisible the speed of light in the vacuum is infinity. crazy? yes. but in a microwave where the wavelength is in the centimeter range it is possible to have materials which perform as a true invisible cloak, similar to the invisible cloak in harry potter but it wouldn't' work if you were moving around.

http://en.wikipedia.org/wiki/Cloak_of_invisibility#Cloaks_of_invisibility_in_science

They have materials that have index n of less than 1 for visible light to, they are called plasmas. And light doesnt travel faster than c in them anyways, your definition is for phase velocity.

You can take picture of this thing if you want to, you just need a very fast camera. How would this by any different from taking a regular picture of the beam, except you just want to take it as the beam starts to propagate through the frame. There are cameras this fast, that are called gated framing cameras. They are used all the time in experiments related to nuclear fusion where things happen on nanosecond timescales. Here is a link to one that can have frame times down to 200 ps.

http://wsx.lanl.gov/Publications/ReallyFast_Camera.pdf

A laser beam would propagate about 2.5 inches in that amount of time. There are probably faster ones out there, but this is the first one that I found on google.
 

Switch

New member
Joined
Dec 9, 2007
Messages
3,327
Likes
4
Points
0
Man , you sure know your lasers :D
So that's very possible then, but the camera would have to take a photo AFTER the beam went past the lens because only then the light reflected from impurities in the air would reach the lens and the camera would see the beam "half way" even though it already got past it.This would work best if the camera was far away from the beam but had a narrow field of view.This is so that the triangle that you were talking about earlier(it would be an isosceles triangle considering the camera and the beam are perpendicular to eachother) will have it's base much smaller than the other sides.This way your "emerging beam video" will be more acurate(but still wrong).
 

diachi

Well-known member
Joined
Feb 22, 2008
Messages
9,447
Likes
1,322
Points
113
cool ::) and my physics teacher was saying i should read more about physics at home ;D well id love to see the laser in slow-mo i dont think there are any vids on youtube though, ill have a look. :)
 

climbak

New member
Joined
Apr 14, 2008
Messages
373
Likes
6
Points
0
Just to clarify the speed of light discussion a little bit. There are materials, as has been previously noted, such as plasma in which the speed of any particular phase of light is travelling faster than c. In fact, the phase speed is always greater than the speed of light in vacuum. However, a single frequency can not carry information. In order to carry information a pulse or beam needs some kind of variation; either frequency or amplitude. The overall group speed of the light is always less than c. The group velocity is the speed at which information can travel and thus no laws of science are broken. Also, for a medium in which light at a certain frequency can propagate faster than c, the absorption of that frequency tends to be so high that even if it were possible to send information this way, the light carrying this information would be absorbed. I think I have some simple plots of phase speed and group speed in a plasma as well as one that shows a material with a negative index of refraction and the corresponding absorption if anyone would like to see them.
 
Joined
Dec 26, 2007
Messages
6,333
Likes
161
Points
0
daguin said:
[quote author=nikokapo link=1209487097/15#18 date=1209513092]
(sorry to digress)
but i always wanted to know
when i shone my laser onto a pool (filled with water..of course), no matter what angle i shone it into it, the angle in which you saw the beam wouldnt dramatically change.
i.e.
i shone it at like 4° from the ground and the angle on the swimming pool was around 75°

WHY
Light travels at a different speed through water.  When the light slows down the object appears to "bend" because you are perceiving it at a different angle.  The difference between the two is refraction.  The refractive index illustrates the degree of difference between the two materials.

Peace,
dave
[/quote]


but what about the minimal angle from the water?
i mean, the "entering" angle had NOTHING to do with the angle of light in the water :S
 

climbak

New member
Joined
Apr 14, 2008
Messages
373
Likes
6
Points
0
nikokapo said:
but what about the minimal angle from the water?
i mean, the "entering" angle had NOTHING to do with the angle of light in the water :S
The angle is due to the different speeds in the different media. The equation describing this is Snell's Law:

n[sub]1[/sub]sin(theta[sub]1[/sub]) = n[sub]2[/sub]sin(theta[sub]2[/sub])  where theta is the angle the ray of light makes with the line that is perpendicular to the surface.

The equation can be derived in many ways but I think in this case the best way to think about it is Fermat's Principle of Least Time which states that light will travel in a medium in such a way as to minimize the overall time it takes to go from point A to B.

EDIT: I had to run to a meeting write as I was finishing this so I forgot something. Because the light travels slower in the water, it will travel at a greater angle to get through the medium more quickly.
 




Top