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 of1x10^-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.