Bessel–like beams with z–dependent cone angles

The conventional means of generating Bessel–Gauss beams by axicons in the laboratory results in the distinct disadvantage of an abrupt change in intensity at the boundary of the non–diffracting region. We outline theoretically and then demonstrate experimentally a concept for the creation of Bessel–like beams that have a z–dependent cone angle, thereby allowing for a far greater quasi non–diffracting propagation region.