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Re: harmonics, anharmonic ...



Hi Ludwik-
The word "explain" is not unambiguous; it depends upon
context. The book <An Introduction to Nonlinear Optics>,
G.C. Baldwin (Plenum 1969) "explains" frequency doubling
merely by observing that there are non-linear terms in the
polarization tensor of the medium transmitting an EM wave.
One can make a simple picture of this by supposing that charge
separation induced by an E-field, like the response of a real
spring, becomes non-linear for large values. So perhaps the real
question should be: Why, for ordinary matter, is the response
(the polarization, or, if you will, the susceptibility) so linear
over a large range of field strengths.
For more intuitive comments at the atomic level, see
the Feynman Lectures, Vol. II, chapters 10 and 11.
***************************************************************
We have only one frequency at the input and two at the
output. I do not see how this can be explained without
addressing the interactions at the submicroscopic level.
To ignore atoms we must have a nonlinear relation
between two macroscopic parameters, like in a diode.
What versus what is macroscopically nonlinear to
explain the appearance of green light?
**************************
Regards,
Jack

"I scored the next great triumph for science myself,
to wit, how the milk gets into the cow. Both of us
had marveled over that mystery a long time. We had
followed the cows around for years - that is, in the
daytime - but had never caught them drinking fluid of
that color."
Mark Twain, Extract from Eve's
Autobiography