The transmitting axicon is examined for the axial field distribution of a regular axicon when the incident wave is plane and uniform, and when it has a gaussian irradiance distribution. In the microwave region, the focal depth of an axicon does not differ very much from that of a perfect lens. In the visible region, the axicon possesses a much greater focal depth, which can be greatly changed by changing the curvature of the slanting side of the axicon. For an axicon with a straight slanting side and small height, when a gaussian incident wave is used, the irradiance at the principal focus varies inversely with the focal length.
John W. Y. Lit and Réal Tremblay, "Focal depth of a transmitting axicon," J. Opt. Soc. Am. 63, 445-449 (1973)