title: A bound for the range of a narrow light beam in the near field.
abstract: We investigate the possibility of light beams that are both narrow and long range with respect to the wavelength. On the basis of spectral electromagnetic field representations, we have studied the decay of the evanescent waves, and we have obtained some bounds for the width and range of a light beam in the near-field region. The range determines the spatial bound of the near field in the direction of propagation. For a number of representative examples we found that narrow beams have a short range. Our analysis is based on the uncertainty relations between spatial position and spatial frequency.
authors: Department of Imaging Technology & Science, Faculty of Applied Sciences, Delft University of Technology, Delft, The Netherlands.
authors: Piet W
authors: PW
authors: Verbeek
authors: Peter M
authors: PM
authors: van den Berg