Mise
isle of lucy
First person to ask the next question asks the next question, IMO...
Science and Technology Quiz 3
- Thread starter Aramazd
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SS-18 ICBM
Oscillator
Yeah, I suppose. Open floor to you guys.
GoodGame
Red, White, & Blue, baby!
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A polarizer. It blocks light moving in waves that are not coherent to the polarizer. Effectively it blocks the the majority of light waves in a non-coherent beam.
Sunglasses are an example.
Perfection
The Great Head.
Pretty sure it's not a polarizer.
A one way mirror might be a good example.
I would imagine that these are useful in producing coherant light (lasers)
A one way mirror might be a good example.
I would imagine that these are useful in producing coherant light (lasers)
GoodGame
Red, White, & Blue, baby!
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One way mirrors are actually a trick of lighting. http://science.howstuffworks.com/question421.htm They reflect some light back, and differences in lighting on opposite sides of the mirror perfect the illusion. But you're right, it is used in lasers.
Not significantly different than a stack of polarizers, in effect, anyways.
Not significantly different than a stack of polarizers, in effect, anyways.
Perfection
The Great Head.
I'm going to guess that the half silvered surface is what he's really talking about.
Polarizers filter the light by polarization, not by direction. They work the same way in both directions.
They usually are a part of the device I am looking for, though.
Half silvered surfaces don't distinguish between directions either.
You're right, the device indeed is usually used together with lasers.
They usually are a part of the device I am looking for, though.
Half silvered surfaces don't distinguish between directions either.
You're right, the device indeed is usually used together with lasers.
Perfection
The Great Head.
Some sort of assymetric lens/prism thing?
No, but usually an effect very similar to the Kerr effect is used.
No, the path a light takes through a lens or prism is reversible. So incoming light coming form a direction where light is emitted will always get through. You can eliminate most of the stray light this way, but not all light.
thetrooper
Misanthrope
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Some sort of collimator?
Mise
isle of lucy
Being as it's uppi's question, it's probably some sort of semiconductor 
No.
Being as it's uppi's question, it's probably some sort of semiconductor
No, this time it isn't a semiconductor. Maybe next time
GoodGame
Red, White, & Blue, baby!
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I'd have thought a Kerr cell would be more practical, but then is the answer...a Pockels cell?
No...it doesn't work with an electric field...
Yes .
Maybe I need to start asking easier questions...
A device that lets light through from one direction but not from the other is called "optical isolator". If laser light is backreflected in a setup, this can act as a larger laser cavity and you get unwanted modes in the laser. A cheap solution is trying to tilt the surface so that the light isn't reflected exactly backwards. However this is not always possible and in such cases you need an optical isolator.
One possibility to build such an optical isolator is the Faraday effect. A (strong) magnetic field parallel to the light is applied to a medium, resulting passing light to have a rotated polarization. But contrary to other devices to rotate the polarization, if the light comes from the other direction it is rotated in the same direction, doubling the total rotation instead of countering it for reflected light.
So how do you build an optical isolator from this? You take two polarizers, rotate one by 45 degrees against the other and put a Faraday rotator set to 45 degrees between them. If light comes from one direction, it will become linearly polarized by the first polarizer, then that polarization will be rotated by 45 degrees by the rotator and then pass the second polarizer. If the light comes from the other direction, it will become linearly polarized with a 45 degree rotation by the second polarizer and then the Faraday rotator will add another 45 degrees so that it is rotated 90 degrees and thus blocked by the first polarizer. So from that direction, no light can make it through.
GoodGame was closest to the answer, so if he wants, he can ask the next question.
A device that lets light through from one direction but not from the other is called "optical isolator". If laser light is backreflected in a setup, this can act as a larger laser cavity and you get unwanted modes in the laser. A cheap solution is trying to tilt the surface so that the light isn't reflected exactly backwards. However this is not always possible and in such cases you need an optical isolator.
One possibility to build such an optical isolator is the Faraday effect. A (strong) magnetic field parallel to the light is applied to a medium, resulting passing light to have a rotated polarization. But contrary to other devices to rotate the polarization, if the light comes from the other direction it is rotated in the same direction, doubling the total rotation instead of countering it for reflected light.
So how do you build an optical isolator from this? You take two polarizers, rotate one by 45 degrees against the other and put a Faraday rotator set to 45 degrees between them. If light comes from one direction, it will become linearly polarized by the first polarizer, then that polarization will be rotated by 45 degrees by the rotator and then pass the second polarizer. If the light comes from the other direction, it will become linearly polarized with a 45 degree rotation by the second polarizer and then the Faraday rotator will add another 45 degrees so that it is rotated 90 degrees and thus blocked by the first polarizer. So from that direction, no light can make it through.
GoodGame was closest to the answer, so if he wants, he can ask the next question.
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