Light amplifier?

[YT2095]

I`v had an idea that may sound a bit Sci-Fi (and might well be) and I wanted to check if it has any scientific merit or plausibility.

 

since light or photons are absorbed and re-emitted when it passes through a clear substance like glass, and the photons that exit aren`t the exact same photons that struck the material I wondered what would happen if the material was charged somehow?

 

IE/ you pass an electrical current through a slice of quartz giving it energy, whilst passing a laser beam through it, will the emitted photons pick up this energy and perhaps Amplify the beam?

 

I was thinking of the photons given off when an element is ionised (yellow for Sodium etc...) and thought that if the electrons are a little above ground state and not actually giving off light themselves as they drop back down, could a Single photon trigger 2 photons to be emitted instead of 1?

[insane_alien]

isn't that ow the photon multiplier tubes in night vision goggles work?

 

edit: yep http://en.wikipedia.org/wiki/Image_intensifier

[YT2095]

an Interesting read, but it`s only Half right, I was thinking something more Solid-State and specific for Lasers.

 

a sort of Hybrid between a gas laser (but using a solid instead of a gas) but still charged with electricity in the same way and bellow any lasing threshold, and then "pumped" with a Laser to trigger it.

a bit like the classic Ruby rod laser, where the mirrors at either end are conductive and have an electrical potential between them.

or in the case of a DPSSFD laser where the frequency doubler crystal has a current passing through it.

[insane_alien]

but if its charged then the atoms are going to be in the excited state, which isn't stable, so it would self trigger like in a normal laser.

[YT2095]

no, not if it was below the lasing threshold.

[swansont]

I`v had an idea that may sound a bit Sci-Fi (and might well be) and I wanted to check if it has any scientific merit or plausibility.

 

since light or photons are absorbed and re-emitted when it passes through a clear substance like glass, and the photons that exit aren`t the exact same photons that struck the material I wondered what would happen if the material was charged somehow?

 

IE/ you pass an electrical current through a slice of quartz giving it energy, whilst passing a laser beam through it, will the emitted photons pick up this energy and perhaps Amplify the beam?

 

I was thinking of the photons given off when an element is ionised (yellow for Sodium etc...) and thought that if the electrons are a little above ground state and not actually giving off light themselves as they drop back down, could a Single photon trigger 2 photons to be emitted instead of 1?

 

 

That's more or less how a laser diode works. In order for there to be amplification, you have to excite the atoms into a state where they can emit a photon of the right energy. What's available is something called a "tapered amplifier" which gives single-pass gain. It's tapered because the beam tends to expand, and that's actually a good thing, as it reduces the power density. You can a factor of 10 or so in amplification, for outputs up to around a half a watt. The ones we have for 852 nm are around x14. (~35 mW in, 450-500 mW out)

 

Something that's clear isn't absorbing the photons, though.

 

 

As for multi-photon emission, it's true that de-excitation can take multiple steps and give multiple photons, but these would be of different energies. An incoming photon would induce a transition of the same wavelength, but typically not for the others AFAIK. It would be interesting, though, to see if you could lase at 2 different wavelengths at the same time (and maybe someone's already done it).

 

but if its charged then the atoms are going to be in the excited state, which isn't stable, so it would self trigger like in a normal laser.

 

Not if you don't have mirrors on it. You'd have spontaneous emission and some gain, but in all directions. If the surfaces had anti-reflection coatings on it you wouldn't get above the lasing threshold (as YT has already said)

[kevinalm]

Something more along the lines of what the op had in mind.

 

There exist optical media that are nonlinear, whose index of refraction is strongly dependant on intensity. If you make an interference cavity out of such a media and setup a destructive interference with a strong monochromatic light source (laser), then you can feed a much weaker 'signal' that varies the output (by changing the index). You then have a light amplifier. I recall reading about it some years ago in an article on 'photonic circuits'. It was proposed as an all optical analog to the transistor. I don't know if anything ever came of the idea. I do believe some actual experiments were done. Sorry, don't have a link.

Edited October 21, 2008 by kevinalm