
282 OPTICS FOR ENGINEERS
• The imaginary part, b, is called the confocal parameter and is related to the beam waist
diameter through Equation 9.21.
• At any location, z, the radius of curvature is given by Equation 9.18. We note that ρ < 0
indicates a converging wave, and ρ > 0 denotes a diverging wave.
• The beam diameter, d, related to b
, is given by Equation 9.19.
• Finally, we note that if any two of the four parameters, d, ρ, z and d
0
are known, then
the others may be calculated.
9.2 GAUSSIAN BEAM PROPAGATION
We begin our discussion of beam propagation by looking at Equation 9.9, which gives us ρ
and b
(or d), from z and b. We can put these into ...