How can you determine the diameter and ring thickness of the beam created with a Plano-Convex (PCX) Axicon Lens?

A Bessel beam is a non-diffractive beam comprised of rings equal in power to one another. Although Bessel beams are only theoretically possible because they require an infinite amount of energy, the output of Plano-Convex (PCX) Axicon Lenses offer a good approximation by maintaining a high level of the non-diffractive Bessel beam properties.

The ring thickness (t) is easily defined by taking ½ of the beam diameter (d_b):

The diameter of the ring (d_r) is defined using the length from lens output to image (L), the index of refraction of the lens material (n), and the angle a: