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I'm studying the article "The Quantum Theory of Optical Coherence" by Glauber (see eg. http://prola.aps.org/pdf/PR/v130/i6/p2529_1), and I've a couple of questions.

1. Why are the arguments of E(+) and E(-) in equation 3.6 two different sets of coordinates? We obtained E(-) by taking the complex conjugate from E(+) (eq. 2.15), so wouldn't it make sense to keep the arguments of those two the same?

2. Glauber sets up a correlation function G

^{n}, but what does this function actually describe? I thought it described the correlation between n points in spacetime, and that correlation and coherence where more or less equivalents. However, Glauber argues that if the wave is actually coherent up to the

*n*th order, G

^{n}should factorize, so the photon detection events are independent, ie. not correlated. So.. if the events are correlated, the wave is not coherent? What then is the relation between correlation and coherence?

3. If all those operators should operate independently, and detection involves the destruction of a photon, does that mean that a fully coherent wave (which, according to Glauber, satisfies an infinite order of coherence conditions), should contain infinite photons?

Thank you!