Jim Kelley wrote:
Cecil Moore wrote:
Remember, these are photonic EM waves.

I'm gonna write that down.

Write this down while you are at it.

In modern physics, the photon is the elementary particle
responsible for electromagnetic phenomena. It mediates
electromagnetic interactions and is the fundamental
constituent of all forms of electromagnetic radiation,
that is, light. The photon has zero rest mass and, in
empty space, travels at a constant speed c;

According to the Standard Model of particle physics,
photons are responsible for producing all electric and
magnetic fields, and are themselves the product of
requiring that physical laws have a certain symmetry
at every point in spacetime.

Nevertheless, all semiclassical theories were refuted
definitively in the 1970's and 1980's by elegant photon-
correlation experiments.

So, should momentum change? Or should we expect it to be conserved?

Momentum is conserved. A change in momentum is a change in
the direction of momentum, not a change in the magnitude.
Hams call that a reflection. What do you call it?

I still like "Cecil's 4th Mechanism of Reflection" best.

If you don't like the word "reflection" for what happens at
a non-reflective thin-film coating, please give me another
word for it. I could easily call the physical happening by
another name. "A rose by any other name ..."

Ask again after you've come to understand the difference between a unit
of measurement and a defined physical quantity.

Jim, in engineering, all watts are power. That's an engineering
convention. I'm sorry that your physicist conventions are different
but amateur radio is part of RF engineering. Sorry about that.
--
73, Cecil, http://www.qsl.net/w5dxp