Slowing of Bessel light beam group velocity

Bessel light beams experience diffraction-limited propagation. A different basic spatial property of a Bessel beam is reported and investigated. It is shown a Bessel beam is a natural waveguide causing its group velocity can be subluminal (slower than the speed of light) when the optical frequency omega approaches a critical frequency omega(c). A free space dispersion relation for a Bessel beam, the dependence of its wave number on its angular frequency, is developed from which the Bessel beam's subluminal group velocity is derived. It is shown under reasonable laboratory conditions that a Bessel light beam has associated parameters that allow slowing near a critical frequency. The application of Bessel beams with 1 mu m spot size to slow down 100 ps to 200 ps over 1 cm length for a natural optical buffer in free space is presented. (C) 2015 Elsevier B.V. All rights reserved.