Module 8 : Laser- II
Lecture   : Rate equations for Lasers
  \includegraphics{gaussian.eps}
  Example:
  A 10 mW He-Ne laser operating at 633 nm has a spot size of 10mm. Assuming a Gaussian beam find the beam radius and intensity at a distance of 100m from the source.
 

Solution:

  The beam radius is half the spot size. The beam divergence (half angle) is given by
$\displaystyle \theta = \frac{\lambda}{\pi w_0} = \frac{633\times 10^{-9}}{\pi\times 5\times 10^{-3}} = 4.03\times 10^{-5}\ \ {\rm rad} = 0.0023^\circ$
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