New kind of light source -- tell me where I'm wrong.

I was playing around with the idea of how you could make an LC circuit that could oscillate at visible light frequencies (600 Terahertz). First of all, since an electrical signal only travels half a micron in the span of a wavelength of that frequency, a circuit with discrete components connected with conductors would never work (unless they were extremely small). But what if the circuit was made up of a single component, which was both the inductor and a capacitor? Even if it was much larger that a micron, could it nevertheless oscillate at 600 Terahertz, since it's only the rise and collapse of the magnetic field and the displacement current that are determining the frequency?

Here's my design. Take a foot-long, 2-inch diameter copper pipe, and bend ends very slightly in the same direction, so it looks like this:


The length of pipe itself should have an inductance of around 50 nanohenries. From modelling the circuit, anything a lot less than that, and it can't sustain the oscillation. This means that to oscillate at 600 Terahertz, it needs a capacitance on the order of

1x10^-12 picofarads! Since the ends of the pipe deviate from the straight line, there should be a tiny component of capacitance between one end and the other. How to calculate that amount, in a scenario like this, I have no idea, but I figure I could figure it out experimentally.

By the simulations I've run, if 16kV were applied across it, say with a spark gap, it would resonate for a good millisecond, discharging half a watt from the induction, half a watt from the capacitance, and negligible power from the DC resistance of the pipe. Supplying it with stimulation every millisecond would provide a constant light source with a tunable frequency.

Is it possible that the full length of metal could oscillate at that frequency, even though it is much larger than the wavelength? Might it cause multiple waves of that wavelength to propagate along it's length? What I'm hoping is that someone here who is more knowledgeable about these things than me can explain why this won't work, if that's the case, so that I can stop wasting time on this idea! :-) Thanks.

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Well, you're basically describing an antenna that's a (large) multiple of the working wavelength long.

Trouble is, such antennas are resonant only if their length remains fairly constant, and copper at shirtsleeve temperatures simply can't stay stable enough length-wise. I'm not going to work out the thermodynamics, but I don't think LN2 would be cold enough to stabilize it.

Mark L. Fergerson

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A single component that is both the inductor and a capacitor is a resonant cavity. Yes, you can get a cavity to resonate if its length is a large multiple of the wavelength at the operating frequency; that's how lasers work.

Reply to
Stephen J. Rush

What a bright idea. I use to do this type of light stuff with great results. Wait until you build your first model and see what color the light ends up as. Your approach is an improvement over mine, you should pursue a patent immediately now that you have disclose it.

Good Luck,

  • * * Christopher

Temecula CA.USA

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One question: even if you can get that high

a frequency, what part of your circuit emits the photons? Electrons can shuffle back and forth all they want as fast as they want; where's the conversion to photons?

Reply to
Randy Day

treat it like a straight pipe, it has capacitance along its whole length, not just at the ends. the capacitace will probably be too high anyway.

a spark gap would be too slow,

have you heard of the skin effect?

I don't think so.

not noticeably at the scaly you are discussing, it'll probably emiot more visible thermal photons than visible radio photons.

to oscilate properly, yes it'd need standing waves.

Bye. Jasen

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How far away are you standing? If you blink, what is the change in frequencies? Try to make a calculation of accuracies involved and then do a test!



Reply to
Stanislaw Flatto

Capacitance is present whenever there is an electric field; the 1-foot pipe doesn't need any bend, because its capacitance doesn't come in parallel-plate form.

Your pipe will resonate, all right, but in the sub- GHz range ( it's about the right size for resonant dipole antenna elements at 400 MHz).

To make a resonator for visible light, one requires something smaller (like an atom), and because of quantum effects, this ends up with a neon light or other similar item. The familiar light sources (incandescent gas in the Sun, hot embers or tungsten filament, maybe some bioluminescence) that we see in nature are at the root of all our light generators. Even LEDs use the same quantum effects as the sodium-doped yellow of a candle flame.

The advent of lasers, though, makes rich fields open up, and the LC oscillator is a part of many light sources nowadays. It just isn't a simple optical-resonance part.

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Others will tell you of the problems with tour assumptions about the pipe's inductance and capacitance but there is a 'systematic' problem to overcome.

First: ask the question How much faster than the speed of light must the light generated by your pipe be able to travel at for this 'system' to work?

Then calculate the answer.

Knowing the problems that you need to overcome will help you find a solution.

Don't give up.

Reply to

Bend or no bend you have a resonant cavity - and a rather low frequency one at that. Klystrons, Gunn oscillators, traveling wave tubes, magnetrons use similar ideas - and don't get up to light frequencies.

There's a "nitrogen laser" that uses an open channel at atmospheric pressure to create laser light . . . . A gas laser that looks like no other and depends on jumping a spark to excite the air in the channel.

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