Hello,

This is essentially the same question I posted in the thread on "FM
Photons", and I've just become more puzzled (and I haven't seen any
replies there). Very simply, if I have a source (a "carrier") of
monochromatic photons (at 800kHz, or at visible light - it's not
important) and I modulate this photon source mechanically, by blocking
and unblocking this source, will I get the same spectrum as if I had
keyed the source on and off? (The spectrum predicted by Fourier
analysis of an amplitude modulated signal - a carrier with sidebands)
And in both situations, why do I get a spread of photon energies? At
least one reply to Radium pointed out that photon energy doesn't
change. But if I put a detector between my source and the mechanical
shutter I believe I will see monochromatic photons, yet the same
detector on the other side of the shutter will see a broader spectrum
- a mixture of the carrier and higher and lower energy photons. Is
this quantum physics at work? Or does Fourier not apply in this
situation, and I will not get any sidebands - just a presence or
absence of monochromatic photons.

I replied to my own question in that thread with my own go at
answering it, but I wouldn't mind seeing a reply from somebody more
cluey! I have a little bit of background in electronics engineering,
so I thought I understood AM.

(I suppose only quite modest resources would be required to test this
- an audio frequency oscillator for the carrier, a metal bladed fan
for the modulation, and an audio pre-amp feeding a computer with some
spectrum analysis software. Not sure about the antenna required to
radiate and pickup a useable signal though)

Yes, you will get the same spectrum.

To understand why, you have to remember photons have both particle
and wave characteristics.

If you look at it as a wave, you're are turning the source on and
off and therefore introducing distortion to an otherwise perfect
sine and generating other frequencies.

On Jun 15, 12:35 pm, j...@specsol.spam.sux.com wrote:
Yes, you will get the same spectrum.

To understand why, you have to remember photons have both particle
and wave characteristics.

If you look at it as a wave, you're are turning the source on and
off and therefore introducing distortion to an otherwise perfect
sine and generating other frequencies.

Okay - I accept what is happening when I treat my photons as waves.
But it seems like magic when treated as particles - how the photons
"know" that there is a moving mechanical gadget in their path, and how
they "know" what their energy distribution needs to be (and that they
are to remain monochromatic until they are on the other side of the
shutter).

But if that's the way the universe works...