Since as was defined earlier, the final wave equation will be
_________ (10)
This equation is the Bessel's equation and solutions of this equation are called the Bessel functions .
Field variation in the transverse plane in the radial direction will be governed by the Bessel's equation and the field distributions would be Bessel functions.
9.
We have a variety of solutions to the Bessel's equation depending upon the parameters
and . is an integer and a positive quantity.
Depending upon the choice of i.e., a) real, b) imaginary, c) complex,
we get different solutions to the Bessel's equation. So to choose the proper solution we must have the physical understanding of the field distribution.
Here we use the physical understandings gathered from the ray model of the light propagation.
as was defined earlier, the final wave equation will be 
_________ (10) 
and 
. 
is an integer and a positive quantity. 
i.e., a) real, b) imaginary, c) complex, 
