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[ATM] Roughness of Ground Surfaces

I found this astonishing quote, can somebody make sense of it?

"In a series of papers published in 1987 [23] E. Wolf considered radiation from
a three-dimensional quasihomogeneous source and showed that if the spectral
coherence of the source i.e. the correlation in the fluctuations of
the source, is
appropriately chosen, the spectrum of the emitted radiation can be redshifted or
blueshifted with respect to that of the source, even when the source
is at rest with
respect to the observer, and the radiation propagates in free space. ..."

This defies my understanding of physics and is mind-blowing.

===========================

I advocate the red-out test.  That is, look at the reflection - at a
grazing angle - of an incandescent lamp.   As the angle of incidence
moves away from 90 degrees, there is a point where the virtual image
of the lamp goes red, and just a little bit further it vanishes.
The angle at which the image vanishes depends on the wavelength and on
the surface roughness, so we could use this as an indication of when
we go to the next grit or to polishing.   Of course the red-out angle
should be the same for all zones of the workpiece, especially at the
edge zone where fine grinding is frequently incomplete.

I think a quantitative test could be done by simultaneously using a
red and green laser.  At a certain angle, there would be a specular
reflection of the red light, but not of the green light.   That angle
could be correlated with surface roughness.
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