A
HeNe laser, radiating
at 632.8 nm, has a
power output of 3.10 mW and
a full-angle beam divergence of
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Solution: Click For PDF Version (a)
The area
subtended by a cone of angular size
Therefore,
the area subtended by the laser beam of full-angle divergence of
The power output of the HeNe laser is 3.10 mW. Therefore, the intensity of the laser beam at a distance of 38.2 m from the laser will be
(b)
The power
output of an isotropic source that will provide the intensity of
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.
We have to find (a)
the intensity of the beam
38.2 m from the laser;
(b) and calculate the power output of an
isotropic source that provides the same intensity at the same
distance.
at a distance r from
its vertex is
.
at a distance of 38.2 m will therefore be