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E/m Field Is Quantizied (=photon Exists In A Vacuum Too).

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Posted by Alexander on October 31, 2001 19:47:03 UTC

Consider simple experiment with Michelson interferometer. Set both mirrors at the same distance from a beam splitter, shine a lser into interferometer and you get nice interference pattern on a screen.

Place a darkened glass between laser and interferometer to reduce intensity of laser light to 108 photons per second (so, the average distance between photons after glass is about c/108 = 3 m) to make sure that there is ONLY ONE PHOTON in the interferometer at a time.

Still you get THE SAME nice interference picture on the screen (but it'll take longer time, so wait a few minutes to accumulate good picture on a photofilm).

No is the main experiment. Move one slit to increase difference in path length. You'll see that the interference picture starts to deteriorate. After the path difference is more than so called coherence length (of e/m wave), no interference is seen at all. Let's say that it took 5 cm in difference between path length in one arm versus another one to make interference pattern disappear. What does this mean? Does not this mean that e/m wave has certain length (=about 5 cm in our particular example, not to be mixed with a wavelength which, say, for red line of He-Ne laser is 0.63 micrometers only), so it propagates as a 5-cm "bunch" in the interferometer thus unable to interfere with itself when arrives back reflected from mirrors with more than 5 cm delay? Is not this "bunch" what we call a photon? And it exists as moving with c bunch of e/m wave of a finite length (called coherence length).

Sun's photons have "length" a few millimeters, but laser photons (of the SAME wavelength) can have length 5 cm, 5 meters, even a few kilometers long (extremely narrow spectral lines).

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