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I have worked with KTP for years and understand how it frequency doubles. I understand that it is an electromagnetic wave propagating in a crystal excites oscillations which converts 1064nm to 532nm (or even tripling to 355nm).

But when asked by a non laser person how it works I find myself unable to come up with a good analogy. Got one for lasers, Q-switching, pockel cells, mode lockers but not KTP.

Does anyone one there have a good one?

I took a few months of doing holograms but I am back now and just made a new batch of DCG film. Looking forward to getting back to it....

Thanks all,
Tony

How's this?

If you don't need to know the math then you just need a diagramitic understanding for which Type I SHG is easier. Two photons of 1064nm light make a single photon of 532nm light because they are passed through a crystal that has different speeds of light based on the angle of polarization (non-linear).

The best analogy I've read was on the laserFAQ. Imagine wave of light passing through the crystal, and pushing the electrons back and forth as it goes. When there isn't too much light, the electrons follow the light and as the photon's energy is absorbed it is re-emitted at the same frequency. But if there is a whole lot of light the electrons get pushed around more violently, and can't keep up. When that happens the photons they emit are at a lower frequency than the incoming light.

Or another analogy from the same page (which I can't find right now...), imagine a sin wave being fed to a speaker. Now turn the volume up. The speaker cone will eventually fail to keep up, and you get distortion, resulting in harmonics. The sin wave gets clipped to a square wave, do an FFT of that and you get harmonics.

Tommy wrote: When that happens the photons they emit are at a lower frequency than the incoming light.

Well it's the opposite...

Tommy wrote:Or another analogy from the same page (which I can't find right now...), imagine a sin wave being fed to a speaker. Now turn the volume up. The speaker cone will eventually fail to keep up, and you get distortion, resulting in harmonics. The sin wave gets clipped to a square wave, do an FFT of that and you get harmonics.

This is the correct analogy. It all happens due to distortion, or non-linearities, which induces harmonics. This is a classical rather than a quantum effect and so it can be easiest described by a light wave rather than in terms of single photons.

Many thanks guys!