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Old 11-29-2006, 02:30 PM #1
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Default Laser pointer beam trapping

I WAS THINKING OF A COOL IDEA 8-)

Lets say you have two mirrors that are perfectly parralel to each other and facing eachother like this:

| | -----(=====)

the (=====) is a laser pointer with a beam going towards the two mirrors at a perfectly straight line and in the middle of them

lets say the mirror on the right had a temporary hole in it, and as soon as the light passed through the hole, the hole would close...

THEORETICALLY...

would it be possible to trap a beam of light between the two mirrors and have it keep bouncing back and forth?

like so:

| <-------> |

if there was a way to get the beam perfectly aligned between the two mirrors... what would happen? would the beam keep bouncing back and forth? if so, how long? light is obviously incredibly fast... therefore the hole idea in the mirror would not work... i do not no if it is even possible to test this experiment

curious what you guys think about this!


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Old 11-29-2006, 05:26 PM #2
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Default Re: Laser pointer beam trapping



Good grief LASEFURY...you have quite an imagination ;D

I reckon that the beam will lose energy like everything else and this would happen in a pico second....to quick to comprehend, so you wouldn't see this trapped beam at all unfortunatly.

What if this was done in a vacuum at -273 Kelvin though......

The mysterious theory of the trapped beam continues.........
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Old 11-29-2006, 06:17 PM #3
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Default Re: Laser pointer beam trapping

there are no 100% reflectivity mirrors, if you had one then this would be possible, otherwise even with a 99.8% reflectivity mirror, the best i think you can get, the beam will be gone a loong time before your slow mind could see it, and no im not calling you stupid :P

if you have ever seen a gas laser working it is generally the same idea, bounces the photons back and forth out of a fully reflective mirror and a semi reflective mirror, some light gets out, but the power inside that tube would be times and times again stronger than the beam getting outputted, abscially like this ((=====)------------------------
where the 2 ((s are the fully reflective mirror and the 1 ) is the semi reflective mirror, the = s are the beam inside the tube, (see its fatter so its stronger rofl) and the ---s are the acual laser output.

sorry to bore you :P

it would be so cool to have a absolute zero room, you could chuck stuff into it and it would disappear XD
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Old 12-07-2006, 10:25 PM #4
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Default Re: Laser pointer beam trapping

Funny you mention this, I used to think of this. Unfortunatly no mirror is perfect, so it won't work. >
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Old 12-09-2006, 03:44 AM #5
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Default Re: Laser pointer beam trapping

1W laser between two perfectly aligned mirrors 1 meter apart, with 95% reflectivity (that's amazing alignment, very strong laser, and high quality mirrors).

In a vaccuum, in theory if you could get the whole 1W between the mirrors, after one micro-second there would be around 0.2 micro-watts of laser left.
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Old 01-19-2007, 10:48 PM #6
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Default Re: Laser pointer beam trapping

As others have pointed out... you can not do this with standard front surface mirrors. *There is no such thing as a perfect physical mirror. Even at 99.999998% coating you quickly lose the beam out that .000002% loss (that is how a ruby laser works, as well as a HeNe laser, etc).

However, perfect mirrors can be created using other methods including electromagnetic entrapment. *But you still have a loss of energy through heat - except in experiments where photons are frozen in place (but in that case the mirror itself is moot as the photons are not actually moving about). *Photons can also be slowed (to an amazingly low rate of speed) and even reversed (so the back edge of the photon wave actually preceeds the starting edge of the wave) - by using exotic materials.

If you like thinking about these things however, consider a deformable mirror (where portions of the mirror can be made to point at different angles at a very high rate of speed) and then making the mirror into a sphere. *(still won't work for all the above reasons but it gets rid of your 'hole' problem. We use deformable mirrors with 188 deformable segments - but even ours need to be cooled to cut down on the heat absorbed from the laser beam itself (this is for an adaptive optics system that we use to remove atmospheric distortion in telescope observations in realtime).
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Old 01-29-2007, 12:51 AM #7
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Default Re: Laser pointer beam trapping

This probably wouldn't work because the light would need a source, the laser. and once you close the hole, there goes the power and the beam, dangit.... that would be pretty cool though... lol I just thought of this... If you had them on a a platform perfectly like this * |<---------->| then you could walk around and it would act like a flash light *;D!!!
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Old 02-09-2007, 07:54 PM #8
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Default Re: Laser pointer beam trapping

What if you angled it EVER SOOO SLIGHTLY so the power could stay on but it would reflect thousands of times between the mirrors before escaping? Not the same as trapping it but I think it would be cool to have 2 miles of visible beam compressed into a 3 foot space... Would this be possible? (maybe it's been done...) :question
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Old 02-09-2007, 09:35 PM #9
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Default Re: Laser pointer beam trapping

Quote:
Originally Posted by stevetexas
What if you angled it EVER SOOO SLIGHTLY so the power could stay on but it would reflect thousands of times between the mirrors before escaping? *Not the same as trapping it but I think it would be cool to have 2 miles of visible beam compressed into a 3 foot space... *Would this be possible? (maybe it's been done...) :question

Yes, indeed... and it is done all the time. Your mirrors need to be near perfect front surface cold mirrors for this to work (else you quickly degrade the beam). These types of systems are used to measure the speed of light (by creating a long enough series of bounces to be able to measure the time between the laser and the final output). Mirrors solve the need to have a very very long pipe etc.
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Old 07-20-2008, 08:00 PM #10
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Default Re: Laser pointer beam trapping

Even if the mirrors would be completely perfect, and even if you could make the light parallell, it won't be possible to have a very powerful laser that bounces back and forth, since we've got the divergence working against everything. After a couple 100 reflections or so, the beam diameter would be REALLY large.

Would've been cool if it would work, though... 8-)
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Old 07-20-2008, 08:18 PM #11
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Default Re: Laser pointer beam trapping

Quote:
Originally Posted by LazerGuy
Even if the mirrors would be completely perfect, and even if you could make the light parallell, it won't be possible to have a very powerful laser that bounces back and forth, since we've got the divergence working against everything. After a couple 100 reflections or so, the beam diameter would be REALLY large.

Would've been cool if it would work, though... 8-)

I run my argon's beam out into the back yard with a series of front surface mirrors. The diameter of the beam by the time it gets to the backyard (about 150 feet) is around 1/2 inch already, but it still diffracts nicely

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Old 07-20-2008, 08:28 PM #12
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Default Re: Laser pointer beam trapping

These are used all the time for getting a high power density out of a low power laser. It is called a power buildup cavity. You shoot in a few 100 mW and you can have kW of power circulating in the cavity. It requires a laser that is stabilized such that an exact number of wavelengths fits in the cavity though. Also these are used all the time for controlling the frequency of a laser. If your laser doesnt have an exact number of wavelength that fit in the cavity the output on the other side of the cavity will be small. so you use a sensor to measure the light output and have it feedback to your and control its frequency. You have electronics adjust the frequency of the laser until the sensor output is maximezed. Once this is true you have locked you lasers frequency to the cavity. It is called cavity locking. It can also be incorporated with other techniques to provide ultrastable laser frequency for making measurements of stuff.

BTW, you use at least one curved mirror, if you are interested just look up stable resonator cavities and it will explain how you do it so the beam stays the same size (also see mode matching)
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