Tim Wescott wrote:

Cecil Moore wrote:

To Jim, and anyone else who wants to discuss it. I've created
a graphic illustrating reflections from a thin-film when the
incident laser beam is at an angle to the thin-film surface.

http://www.qsl.net/w5dxp/weblaser.GIF

Question for Jim: I can see Reflection A and Reflection B.
I can measure the irradiance of Reflection A and Reflection B.
Are the two reflections really there or not? If they are there,
do they possess energy and momentum?

That will get us started.


It doesn't show up on my web browser. Do you have the URL right?

If you have a photon zinging through space it posseses both energy and
momentum, and they are each an easy function of the wavelength.

To pick nits, if you have a _stream_ of photons zinging by it will
posess, on average, power and thrust (or whatever the time-derivative of
momentum is called). If reflections A and B are both there they will
each carry a certain amount of power and exert a certain thrust somewhere.

If you have actually set up this thin film experiment and measured two
seperate reflections then they are indeed there. You can debate whether
the reflections are truely reflective of the theory that you're trying
to demonstrate or if they reflect (or perhaps reflect off of?)
imperfections in your experimental setup.


OK, now I can see your post. Yes, those reflections are real, and the
numbers are probably about as good as you'll get from clean AR coated
glass, IFAIK (_dirty_ AR coated glass will give you much larger
reflections). Laser rangefinders get one heck of a return when they
fire, and are limited in the minimum range that they can measure because
of the time that it takes for the receiver to recover (or be turned on,
depending on the LRF architecture).

I'm confused by your confusion -- what are you trying to do, and why do
you have to ask?

--
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com