Re: inverse square law and "perfect" laser


Salmon Egg wrote:
On 11/21/06 10:03 AM, in article
1164132208.228034.263790@xxxxxxxxxxxxxxxxxxxxxxxxxxxx, "Gary Jefferson"
<garyjefferson123@xxxxxxxxx> wrote:

Laser light obeys the inverse square law, but is this *only* because
the diameter of the laser beam increases linearly (at distance), or is
there something else fundamental going on to decrease light energy as
it travels?

I suppose another way to ask the same question is, in a perfect vacuum,
do all the photons that a central source emits make it to the edge of
some distant sphere, or are there other effects that cause the photon
waves to dissipate or interfere (e.g, cancel out) as they travel?

Although others have answered your question, they were not blunt enough.

Laser beams do not obey the inverse square. They obey the inverse square law
as an approximation for very large distances.

Bill
-- Fermez le Bush

Just to add, trying to stay blunt: conservation of energy is the rule.
Laser intensity is inversely proportional to beam area. Only when the
beam area obeys the square-law will intensity obey the inverse-square
law.

Mark

.

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