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LAN_403

Physics Junkie

Sat Jun 08 2013, 06:48AM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

A wacky question, but here I go:

Hypothetically, you have a Tesla coil that has a resonant frequency somewhere between 400THz and 800THz. Would it emit light?

Ash Small

Sat Jun 08 2013, 10:00AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Every functioning Tesla coil I've seen emits light

Dr. Dark Current

Sat Jun 08 2013, 10:38AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

:-D

The length of wire for such a Tesla coil secondary would be around 100 nanometers. Rather use an LED

Physics Junkie

Sat Jun 08 2013, 11:29AM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

:-D I know but, I'm thinking in terms of electromagnetic energy and frequency. After all, we build Tesla coils resonant in the RF spectrum which give off RF radiation generously. Would a Tesla coil in the visible light spectrum radiate light similarly? Different light than from the plasma discharge, of course

Steve Conner

Sat Jun 08 2013, 12:26PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

This 400THz Tesla coil already exists, it's called a laser.

Some pulsed lasers are powerful enough that when the beam is focused down, the electric component of the field is strong enough to ionise air. The result is a tiny sphere of plasma floating at the lens's focal point. No breakout point required!

Lasers capable of doing this tend to be near infrared, but there's no theoretical reason why it wouldn't work with visible light.

Uspring

Sat Jun 08 2013, 01:41PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

Physics Junkie wrote:

Would a Tesla coil in the visible light spectrum radiate light similarly?

Yes, even coherent light, if the bursts are long enough.

Steve Conner wrote:

This 400THz Tesla coil already exists, it's called a laser.

That tempts me to ask, if a laser is more like a SGTC or a DRSSTC? But seriously, a TC is somewhat similar to a one atom laser, where a single atom (secondary) is pumped by a high frequency field (primary).
The main difference is, that a laser uses only a single excitation of an atom, while a tank is multiply excited.

Steve Conner

Sat Jun 08 2013, 03:55PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I think a laser is similar to a Tesla coil because it is using a resonant cavity to create an EM field. From a functional point of view, the laser cavity is analogous to the secondary coil, even if it looks nothing like one.

If you did what you had to do to push the SSTC concept to 400THz, you'd have a diode laser. The tiny cavity is integrated on the chip and pumped by a "feedback driver" made of individual semiconductor atoms.

Physics Junkie

Sat Jun 08 2013, 07:45PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Steve Conner wrote ...

I think a laser is similar to a Tesla coil because it is using a resonant cavity to create an EM field. From a functional point of view, the laser cavity is analogous to the secondary coil, even if it looks nothing like one.

Makes sense. When you say laser, I immediately think 'straight beam of light'. Now, whether or not it's a focused beam doesn't matter, who cares. That depends if you have a lens of some sort or whatever it takes to focus the light. But still, beam. Light is a wave of oscillating electromagnetic fields perpendicular to the direction itâ€™s travelling which is a straight line. I'm still thinking about it in the point of view of EM waves. The field lines don't exist, duh. But how do you know the direction which the light travels constituting it as a laser-like beam?
I sketched up this weird tiki-voodoo-guy-looking diagram of a Tesla coil and the EM lines

. Now I could have drawn this totally inaccurate in regards to the direction of the EM lines, and I probably did. But you get the point and this is how I am thinking:

I think I sort of get what you mean by a laser (beam) vs. a big haze of red awesomeness. The way I was thinking the photons radiate off the Tesla coil in all directions, like in my diagram.

When you say

resonant cavity to create an EM field

the secondary is the resonant cavity in this case just like you said analogous to the laser cavity. So photons would be generated inside the secondary thus beaming out the top in a straight laser-like beam vs. radiating outside of the "resonant cavity" like how I drew it in the picture? (basically the photons would just be emitted along the axis of symmetry out the top travelling in one direction only, vertical)

Steve Conner

Sat Jun 08 2013, 09:10PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

A Tesla coil is physically small compared to the wavelength it operates at, so it doesn't have any directionality. On the other hand, the laser cavity is large compared to the wavelength, so it shows strong directional behaviour. For a "haze of red awesomeness" it might be possible to make a spherical cavity that would lase in all directions, but it would be an engineering nightmare. And in fact the strong directional behaviour of lasers is one of the properties that makes them useful. The spherical laser would be nothing but a coloured light bulb with an annoying speckle.

Uspring

Sun Jun 09 2013, 02:38PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

As Steve said, a usual TC is small compared to the wavelength. That makes it a dipole radiator.

Most of the energy goes off perpendicular to its axis, nothing along the axis. Lasers are coupled EM systems like TCs, but you shouldn't carry the analogy too far.

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