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to determine the focused spot size,
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to determine the beam radius at some arbitrary point in space, where wF is the radius of
the beam at the focus, and , and wL is the radius of the beam at the focusing
lens. (This assumes that the beam entering the lens is collimated.) M 2can be assumed
to be unity for a theoretical Gaussian beam.
The equation
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is obtained by differentiating the previous equation with respect to distance and setting the result equal to zero.
Remember that, in this equation, w(z) and
w0 are the radii of the real-world beam, not the theoretical Gaussian.
In the second example set, we discuss the problems associated with collimating the highly astigmatic beam of a
typical diode laser.
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