Relative enhancement of on-axis energy backflow in the focused fields via higher-order Laguerre- Gaussian beams

We propose a facile method for enhancing on-axis energy backflow relative to forward energy flow in the focused fields. By employing higher-order Laguerre-Gaussian (LG) complex amplitude profiles for left-handed circularly polarized vortex beams, we numerically demonstrate the proposed method. It is shown that for incident LG beams with a beam size parameter <i>β</i>_4<i>σ</i>⩾1, the ratio of the peak absolute values of the Poynting vector for backward and forward energy flow increases with the radial index <i>p</i> of LG beam and the numerical aperture (NA) of the aplanatic lens. More remarkably, the area of on-axis energy backflow is simultaneously found to be more elongated for larger values of <i>p</i>. Besides, we further show the relative enhancement of on-axis energy backflow in the focal fields of second-order radially polarized LG beams with higher values of <i>p</i>. A similar enhancement effect is actually applicable to other light beams. These results hold potential applications in optical manipulation and sorting.