# Problem: A laser beam has intensity I0. a. What is the intensity, in terms of I0, if a lens focuses the laser beam to 1/10 its final diameter? b. What is the intensity, in terms of I0, if lens defocuses the laser beam  to 10 times its initial diameter?

###### FREE Expert Solution

The intensity of a wave:

$\overline{){\mathbf{I}}{\mathbf{=}}\frac{\mathbf{P}}{\mathbf{A}}}$

Area A = πr2

Intensity is inversely proportional to area.

(a)

Since power is conserved:

P1 = P0

I1A1 = I0A0

A = π(d/2)2

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###### Problem Details

A laser beam has intensity I0.

a. What is the intensity, in terms of I0, if a lens focuses the laser beam to 1/10 its final diameter?

b. What is the intensity, in terms of I0, if lens defocuses the laser beam  to 10 times its initial diameter?