Virtual source for the Bessel–Gauss beam

The virtual source for generation of the fundamental scalar Bessel–Gauss wave is identified. An expression is derived for the Bessel–Gauss wave, which, in the appropriate limit, yields the paraxial approximation for the fundamental Bessel–Gauss beam. For the azimuthally symmetric beam, the first-order nonparaxial correction to the on-axis field is also determined. This nonparaxial correction reduces correctly to that of the fundamental Gaussian beam in the appropriate limit.