title: Creation of a 50,000λ long needle-like field with 0.36λ width: comment.
abstract: In a recent paper, a method for the generation of a long, narrow needle of light was proposed [J. Opt. Soc. Am. A31, 500 (2014)10.1364/JOSAA.31.000500JOAOD61084-7529]. The authors missed fundamental aspects of the mathematical physics of cylindrical electromagnetic waves described by Bessel functions that are essential to obtain the proposed needle. We provide formal arguments showing that a different initial condition is the proper one for the intended purpose. Based on their proposed method we bring to attention the validity of Huygens' principle for cylindrical waves. Also, we extend their analysis in order to have a component of longitudinal energy flow that is needed for most of the applications they suggest. We quantitatively show that a minor modification produces this component with practically negligible increase of the needle width.
authors.forename: Sabino
authors.initials: S
authors.lastname: Chávez-Cerda
authors.forename: Jixiong
authors.initials: J
authors.lastname: Pu